Rules of Cutting Hair in Hajj and ‘Umrah
Question

I completed the rituals of ‘Umrah during Ramadan, and I cut my hair, some from the front and some from the back, and some from the right and left. Is my ‘Umrah valid or not?
Praise be to Allah.Shaving or cutting hair after ‘Umrah?
The jurists unanimously agreed that shaving the entire head is preferable to cutting the hair. It is proven that the Messenger of Allah (peace and blessings of Allah be upon him) shaved his entire head, and he prayed for those who shaved their heads three times, and for those who cut their hair once.  (Al-Mawsu’ah al-Fiqhiyyah, 18/98) 
How much hair should you trim after ‘umrah?
But they differed as to the minimum amount that is acceptable in shaving the head and cutting the hair. The Malikis and Hanbalis are of the view that it is not sufficient to shave only part of the head , because the Prophet (peace and blessings of Allah be upon him) shaved his entire head, and his action explained his command to shave. 
The Hanafis are of the view that it is sufficient to shave one quarter of the head , but if less than one quarter is shaved, that is not sufficient. 
The Shafi’is said that the minimum that is sufficient is three hairs, whether it is shaved or cut. 
Ibn Qudamah (may Allah have mercy on him) said in al-Mughni (3/196): 
“He must cut or shave all of his hair, and the same applies to women . This was stated by Imam Ahmad, and it was the view of Malik. It was narrated from Ahmad that part (of the head) is sufficient. Al-Shafi’i said: It is sufficient to cut three hairs. Ibn al-Mundhir favoured the view that if a man cuts the hair in a manner that may be regarded as hair cutting, it is sufficient. But Allah says (interpretation of the meaning): “having your heads shaved” [al-Fath 48:27]. This is general in meaning. And the Prophet (peace and blessings of Allah be upon him) shaved his entire head, which explains the command to shave the head.”
It says in al-Taj wa’l-Iklil (4/181), which is a Maliki book:
“Whoever shaves his head or cuts his hair, let him do that to his entire head; it is not sufficient to limit it to only part of it.”
Undoubtedly this view is more on the safe side. A person should not limit himself to removing hair only from the front or the back or the right or the left as you have done. 
Cut a small portion of my hair short: Is ‘Umrah valid?
If a person has removed only some of his hair , his case must be examined further. 
If he did that because he was following a scholar who issued a fatwa to that effect, there is no sin on him. 
If he did that based on his own ideas, then this is not sufficient, and he is still in ihram and has not exited it. So he has to remove his sewn garments now, and shave his entire head or cut his hair all over. Thus he will exit ihram, and he does not have to offer any (expiation) for anything that he did during this time of the things that are forbidden when in ihram, because he was unaware of the ruling. 
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) was asked about a man who cut his hair on one side only after doing ‘Umrah, then he went back to his family and he found out that what he had done was not correct. What should he do? 
He replied: 
“If he did this out of ignorance, then he has to take off his clothes now and put on his ihram garments, and shave his head completely or cut his hair, but what he did may be forgiven, because he was unaware. Shaving or cutting the hair does not necessarily have to be done in Makkah, rather they may be done in Makkah or elsewhere. But if he did that based on a fatwa from a scholar, then he does not have to do anything, because Allah says (interpretation of the meaning): “So ask of those who know the Scripture , if you know not” [al-Nahl 16:43]. Some scholars think that cutting hair from part of the head is like cutting the hair all over the head.” (Al-Liqa al-Shahri, no. 10) 
And Allah knows best.