Should I go intimidate a girl that thought I was gay ?
Are you scared of being known as gay?
I'm not scared of my sexuality. Why would I be?
If she was planning to hurt you socially due to your sexuality, then she is in the wrong. Your sexuality is something you can't control and it's wrong to bully people based on sexuality.
Okay, I'll admit it wasn't my best idea. I'm stupid.
You shouldn't think of yourself as stupid, instead realize this was a moment of learning. Situations like this help you to learn and grow as a person.