ANSWER:

If you hadn’t started reciting Attahiyat when you first sat, there was no need to do sujood as sahu and you should have prayed normally.

It was totally wrong to have repeated the salah.

QUESTION: Months ago during prayer, after the first rak‘ah I mistakenly sat for tashahhud, then stood up and completed the salah. I performed sujood as-sahw before tasleem, but later repeated the salah again just to be safe, without asking anyone. Should I do anything now?