Could you tell me if this situation sounds like I accidentally cheated on my girlfriend?
How did you accidentally cheat?
I went to a strip-club with some bros.
Although some some people may be alright with their partner going to a strip club, if yours is not then what you did is wrong. Many people would view what you did as a form of cheating, especially without permission, and you should not do that. Your partner would be very hurt if they don't think it's acceptable for you to go to a strip club.
I think she is fine with it. It was just going to a strip-club with my bros.
If she's fine with it, then there's no problem and it's not really cheating. Just be sure to stick with the sorts of things you have agreed on, and you will be fine.