I remember three times that I said something completely opposite of what I wanted to say for no reason at all. I'm still in school so forgive me for not having anything relevant to real life to mention. Hopefully it helps you feel normal.
I told a Japanese person I hated Chinese people in a conversation simply because I heard that Chinese and Japanese people didn't get along. I don't hate Chinese people.
I downplayed my own expertise when it was called into question when I was on the stand as a witness in Mock Trial in state competition.
I sarcastically said, "Oh no, I'm not in my seat when the bell rang. I'm gonna get a detention," instead of saying, "Crap, I gotta get to my seat!" at the beginning of class.
None of these things I did changed my life significantly. No one heard me say I hate Chinese people, my side of our Mock Trial team won anyways, and all I got for mocking the teacher was the detention that I was going to receive in the first place.
Nonetheless, I would like to shoot myself in the head for saying such idiotic things. I have no idea how these things came out of my mouth. I just wasn't thinking.
There's no way to remove these bad memories, and that is a good thing. If you forget that you may have ruined a relationship by doing what you did, you may do it again.

You have to learn from your mistakes. Do what you can to fix the problem, but don't put yourself in this situation again.