A Catholic woman promised Allah that she would not get married if Allah forgave her sins, then she became Muslim
Question

                I must say that I'm a revert, Alhamdullila, that I was raised as a catholic and that I was very ungrateful to my Rabb before Islam. Since I was a little kid I was mischievous and often committed sin. After one particularly grave sin, and I asked Allah Subhana wa ta'ala (even thought I was a kaaffir I prayed to Allah azza wa jalla and not Jesus, peace be upon him) to have mercy on me, and I promised Him not to marry if He forgave me. Now that I'm Muslim, Alhamdulillah, I protect my chastity. I know the importance of marriage and the protection it offers a sister, and I wish I could get married in the future to a righteous brother (insha'Allah) so I could learn from him and also to be a comfort for him. But I don't know if I'm excused of not fulfilling my promise to Allah in this matter or if a woman who used to be so wicked could aspire to marry a righteous man.
Praise be to Allah.The best thing we can do is start by focusing on the last part of your question in this brief answer. That is where you wonder whether a woman like you who had committed various kinds of sins and now wants to marry a righteous man can do so. This is according to what you say. 
We say to you that no one on the face of the earth can come between you and sincere repentance to Allah, may He be glorified and exalted, or prevent the mercy and forgiveness of Allah from reaching you, or prevent His being pleased with the new direction you are taking. Allah, may He be glorified and exalted, has told us in His holy Book of everything that fills our hearts with reassurance and hope, as He says (interpretation of the meaning):
“Say: O My slaves who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allah, verily Allah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful.
And turn in repentance and in obedience with true Faith (Islamic Monotheism) to your Lord and submit to Him, (in Islam), before the torment comes upon you, then you will not be helped.
And follow the best of that which is sent down to you from your Lord (i.e. this Qur’an, do what it orders you to do and keep away from what it forbids), before the torment comes on you suddenly while you perceive not!
Lest a person should say: ‘Alas, my grief that I was undutiful to Allah (i.e. I have not done what Allah has ordered me to do), and I was indeed among those who mocked (at the truth! i.e. La ilaha ill-Allah (none has the right to be worshipped but Allah), the Quran, and Muhammad SAW and at the faithful believers, etc.)’
Or (lest) he should say: ‘If only Allah had guided me, I should indeed have been among the Muttaqoon (pious and righteous persons).’
Or (lest) he should say when he sees the torment: ‘If only I had another chance (to return to the world) then I should indeed be among the Muhsinoon (good-doers).’
Yes! Verily, there came to you My Aayaat (proofs, evidences, verses, lessons, signs, revelations, etc.) and you denied them, and were proud and were among the disbelievers.
And on the Day of Resurrection you will see those who lied against Allah (i.e. attributed to Him sons, partners, etc.) their faces will be black. Is there not in Hell an abode for the arrogant ones?
And Allah will deliver those who are the Muttaqoon (pious) to their places of success (Paradise). Evil shall touch them not, nor shall they grieve.
Allah is the Creator of all things, and He is the Wakeel (Trustee, Disposer of affairs, Guardian, etc.) over all things.”
[az-Zumar 39:53-62]. 
And our noble Messenger (blessings and peace of Allah be upon him) has told us a hadeeth that every Muslim should memorise and keep in mind so that he might live in contentment, turning to his most generous Lord, may He be glorified. The Prophet (blessings and peace of Allah be upon him) said: “Allah, may He be glorified and exalted, said: ‘O son of Adam, so long as you call upon Me and put your hope in Me, I shall forgive you for what you have done, and I shall not mind. O son of Adam, were your sins to reach the clouds of the sky and were you then to ask forgiveness of Me, I would forgive you and I would not mind. O son of Adam, were you to come to Me with an earthful of sins and were you then to face Me, ascribing no partner to Me, I would grant you forgiveness as great as it.”
Narrated by at-Tirmidhi in as-Sunan, (3540. He said: (It is) hasan ghareeb. It was classed as saheeh by Shaykh al-Albaani in Saheeh at-Tirmidhi. 
What we fear most for you is that the Shaytaan may try to remind you of your past sins so that you might end up despairing of the mercy of Allah, or that he might make you go back to that dark past. 
Rather what you must do now is turn to your Lord, may He be glorified and think positively of Him, with great hope of His bounty and blessing to you. You should put the past behind you and enter the world of Islam which encompasses lands and people with mercy and compassion, as our Lord, may He be glorified and exalted, says (interpretation of the meaning):
“Allah wishes to make clear (what is lawful and what is unlawful) to you, and to show you the ways of those before you, and accept your repentance, and Allah is All-Knower, All-Wise.
Allah wishes to accept your repentance, but those who follow their lusts, wish that you (believers) should deviate tremendously away from the Right Path.
Allah wishes to lighten (the burden) for you; and man was created weak.”
[an-Nisa’ 4:26-28]. 
You should understand that by becoming Muslim and by leaving behind the deeds of jaahiliyyah (ignorance) and shirk (associating partners with Allah), by giving up the sins of the past and repenting to your Lord, may He be glorified and exalted, you have turned over a new leaf before your Lord. Islam (becoming Muslim) erases everything that came before it; all you have to do is keep that new leaf or new page clean and not go back to those sins that have caused you so much grief and that you now regret. 
One of the signs of Allah’s mercy to us is that He does not accept any pledge or promise from us that is contrary to His laws. Refraining from getting married in an attempt to draw closer to Him is not an act of obedience or worship; rather it is contrary to His laws. The Prophet (blessings and peace of Allah be upon him) heard one of the people say that he had chosen to be celibate and devote himself to worship, and he had decided not to get married. But the Prophet (blessings and peace of Allah be upon him) said: “By Allah, I am the one who fears Allah the most among you and the one who the most aware of Him, but I fast and I do not fast, I pray and I sleep, and I marry women. Whoever turns away from my Sunnah is not of me. Narrated by al-Bukhaari (5063), Muslim (1401). And it was narrated that Sa‘d ibn Abi Waqqaas (may Allah be pleased with him) said: The Messenger of Allah (sa) forbade ‘Uthmaan ibn Maz‘oon be celibate; if he had given him permission to do that, we would have gotten ourselves castrated. Narrated by al-Bukhaari (5073). Ibn Hajar said: What is meant by celibacy here is to cut oneself off from marriage and what it brings of physical pleasure in order to focus on worship. End quote from Fath al-Baari, 9/118 
Your refraining from getting married in order to focus on worshipping Allah, may He be exalted, is not part of the religion of Islam; rather it is part of the religion of jaahiliyyah (ignorance), or it is one of the things that were abrogated of the laws of previous nations. If a person swears an oath or makes a promise to Allah, may He be glorified and exalted, that he will refrain from getting married as a means of drawing closer to Him, his oath is invalid and his promise is idle speech that carries no weight, whether he swore that oath before becoming Muslim or afterwards. The Prophet (blessings and peace of Allah be upon him) said: “Whoever swears an oath to commit an act of disobedience, that oath does not count.” Narrated by Abu Dawood in as-Sunan (2191); classed as hasan by al-Albaani in Saheeh Abi Dawood. It was also narrated from ‘Aa’ishah (may Allah be pleased with her) that the Prophet (blessings and peace of Allah be upon him) said: “Whoever makes a vow to do an act of obedience to Allah, let him do it; whoever makes a vow to commit a sin  Him, let him not do it.” Narrated by al-Bukhaari (6696). 
We congratulate you on your becoming Muslim and we congratulate you for having been guided to the straight path. We hope that you will have a happy marriage to a righteous man, by Allah’s leave. There is no sin on you if you break the promise that you made to Allah, may He be exalted, because it is a promise that is blameworthy in and of itself, so you do not have to fulfil it; the expiation for that is feeding ten poor persons, giving each one a meal based on the people’s staple food, or giving the equivalent value in cash. This has been explained in fatwas no. 21833 and 20419. 
And Allah knows best.