He forgot one circuit of tawaaf so he did it after completing saa‘i
Question

I circumambulated the Ka‘bah (tawaaf) when doing ‘umrah, and I did six circuits by mistake, because I forgot that tawaaf is seven circuits. I remembered that during saa‘i, so I did the last circuit after I had completed saa‘i. Do I have to do anything?
Praise be to Allah.Firstly:
Tawaaf for ‘umrah or Hajj must be seven circuits; anything less than that is not acceptable, because Allah, may He be exalted, enjoined tawaaf when He said ( interpretation of the meaning): “…and [let them] perform Tawaaf around the ancient House” [al-Hajj 22:29].
The Prophet (blessings and peace of Allah be upon him) explained that by his actions: he did seven circuits around the Ka‘bah, and he said: “Learn from me your rituals [of Hajj and ‘umrah].” Narrated by Muslim (2286).
An-Nawawi (may Allah have mercy on him) said: The condition of tawaaf being valid is that it should be seven circuits, each time being from the Black Stone to the Black Stone. If a single step of the seven is omitted, his tawaaf does not count, whether he remains in Makkah or departs and travels back to his homeland, and that cannot be compensated for by offering a sacrifice or otherwise." (Al-Majmoo‘  8/21)
Secondly:
Doing the circuits consecutively is a condition of tawaaf being valid according to the Maalikis and Hanafis. If there is a lengthy interval between circuits, then tawaaf must be repeated.
It says in Kashshaaf al-Qinaa‘ (2/483): If tawaaf is interrupted and the interruption is lengthy according to what is customary, and even if it was due to forgetfulness or a valid excuse, then the tawaaf is not valid, because the Prophet (blessings and peace of Allah be upon him) did the circuits of tawaaf consecutively, and he said: “Learn from me your rituals [of Hajj and ‘umrah].”.
End quote.
See also: Mawaahib al-Jaleel (3/75); al-Mawsoo‘ah al-Fiqhiyyah (29/132).
In Fataawa al-Lajnah ad-Daa’imah (11/253) it says: If the pilgrim does tawaaf al-ifaadah and forgets to do a circuit, and there is a lengthy interruption, then he must repeat tawaaf (from the beginning), but 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 sa‘i before tawaaf, and that if it is done before tawaaf, it is not valid.
Ibn Qudaamah (may Allah have mercy on him) said in al-Mughni (3/194): Sa‘i should follow tawaaf, and is not valid unless it is preceded by tawaaf. If someone does sa‘i before tawaaf, it is not valid. This is the view of Maalik, ash-Shaafa‘i and as-haab ar-ra’y. End quote.
Based on that, your doing the seventh circuit of tawaaf after finishing sa‘i does not count, because of the lengthy interruption between it and the other circuits.
Similarly, your sa‘i does not count either, because it was done before finishing tawaaf.
Based on that, you are still in a state of ihraam now, and you must avoid all things that are forbidden whilst in ihraam; you must go back to Makkah and do tawaaf and sa‘i, then shave your head or cut your hair, and thus you will have completed your ‘umrah.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked about a woman who did tawaaf al-ifaadah with six circuits, but she thought that she had done seven. After doing sa‘i and cutting her hair, she did a single circuit. Is that permissible?
He replied: If she is certain that it was six circuits, adding a seventh circuit after a lengthy interval is of no avail. She must now repeat tawaaf from the beginning, with seven circuits. But if it was mere uncertainty after having completed tawaaf, and she only thinks that it may not have been complete, then she should not pay any attention to that." (Majmoo ‘ Fataawa ash-Shaykh Ibn ‘Uthaymeen 22/293).
And Allah knows best.