He forgot one circuit of tawaf and he did it after completing saa’i
Question

I circumambulated the Ka’bah in ‘Umrah, and I did six circuits, because I forgot that tawaf is seven circuits. I remembered that whilst I was doing saa’i, so I did this circuit after I completed saa’i. Do I have to do anything?.
Praise be to Allah.tawaf for ‘umrah or Hajj must be seven circuits, and it is not acceptable to do less than that, because Allahhas enjoined tawaf and said: “and circumambulate the Ancient House (the Ka‘bah at Makkah)” [al-Hajj 22:29]. 
And the Prophet (peace and blessings of Allahbe upon him) explained that by his actions, and he did seven circuits and said: “Learn from me your rituals of Hajj.” Narrated by Muslim (2286). 
Al-Nawawi (may Allahhave mercy on him) said: The condition of tawaf is that it must be seven circuits, each one starting and ending at the Black Stone. If one step of the seven is omitted, then his tawaf does not count, whether he stays in Makkah or has departed and returned to his homeland, and it cannot be rectified by offering a sacrifice or anything else. End quote from al-Majmoo’ (8/21). 
Secondly: 
Doing the seven circuits without interruption is a condition of tawaf being valid according to the Maalikis and Hanbalis; if there is a lengthy interruption between any two circuits, then tawaf must be repeated. 
It says in Kashshaaf al-Qinaa’ (2/483): If tawaf is interrupted by a lengthy interval or because they forgot or because of some excuse, then it is not acceptable, because the Prophet (peace and blessings of Allahbe upon him) did the circuits of tawaf one after another, and he said: “Learn from me your rituals of Hajj.” End quote. 
See also: Mawaahib al-Jaleel (3/75) and al-Mawsoo’ah al-Fiqhiyyah (29/132). 
It says in Fataawa al-Lajnah al-Daa’imah (11/253): If the pilgrim does tawaf al-ifaadah and forgets one of the circuits, and there is a long interval, then he must repeat tawaf. If the interruption is brief, then he may do the circuit that he forgot. End quote. 
Thirdly: 
The majority of fuqaha’ (including the four imams) are of the view that it is not permissible to do saa’i before tawaf, and that if a person does saa’i before tawaf, it is not acceptable. 
Ibn Qudaamah (may Allahhave mercy on him) said in al-Mughni (3/194): Saa’i comes after tawaf, and it is not valid unless it is preceded by tawaf. If saa’i is done first, it is not valid. This is the view of Maalik, al-Shaafa’i and as-haab al-ra’i. End quote.  
Based on that, your doing the seventh circuit of tawaf after finishing saa’i does not count, because of the lengthy interruption between it and the other circuits. 
Similarly your saa’i does not count because it was done before completing tawaf. 
Based on this, you are still in ihraam right now, and you have to avoid all the things that are forbidden in ihraam, and go back to Makkah to do tawaf and saa’i, then shave your head or cut your hair, and thus your ‘umrah will be over. 
Shaykh Ibn ‘Uthaymeen (may Allahhave mercy on him) was asked about a woman who did tawaf al-ifaadah with six circuits, thinking that it was seven. After doing saa’i and cutting her hair, she did one more circuit. Is that permissible? 
He replied: If she was certain that it was six circuits, then doing the seventh circuit after a lengthy interruption is of no benefit. Now she has to repeat tawaf from the beginning, with seven circuits. But if she was merely uncertain after finishing tawaf, and she thought that she had not completed it, then she should not pay any attention to this. End quote from Majmoo’ Fataawa al-Shaykh Ibn ‘Uthaymeen (22/293). 
And Allahknows best.