I'm going to comment that some of the cosplayers looked like guys.
Do you think it's wrong for guys to dress in cosplay?
I was wrong about that and I should apologize to them
Insulting the appearance of people dressing up in cosplay isn't appropriate behavior, especially when the insults are related to their perceived gender. It's good that you recognize your behavior was wrong and that you want to apologize to the people you insulted. In the future, it would be good to avoid commenting on people's appearance in a judgmental manner as that is inappropriate.
It's quite a bad situation now, I'm pretty intimidated by someone.
What your feeling is understandable. It's great that you understand what went wrong. You can always try have a conversation with someone to help you feel less uncomfortable.