"before I oops do it again" or "before I oops did it again again", which one should I have used for it to be proper English?
Solution 1:
Oops! or whoops! is just an exclamation you make when you fall or knock something over, or to acknowledge that you have made a mistake. So putting it in the middle of a sentence as you did doesn't really work, but of course your cousin would understand that you were imitating the words of the song. You could have said
... before - oops! - I do it again.