If you could have ONE do-over in your life....what would it be?

The only thing I can think about is trying to teach my ex gf about the bible, i wish I could do it in a way that convinced her, but maybe we were too immature both for it. I would love to marry her, but instead we broke up right before going into highschool... she was a pretty girl, both outside and inside, but the last strongest memory i have of her is her screaming out "fuck god". It saddens me, I believe we were like made for each other.