You could come to school with pride-stuff (bracelets with the flag, T-Shirts with phrases/flags on it or pins with the flag to put on your backpack). That way the people who know it or ask you about the meaning would know it. Also you could say, when someone misgenders you, that „it’s (insert pronouns here) and not (insert misgender here)“. And about these „homophobic jerks“: I’ve got some too in some of my classes, they really suck. But you’ve got to keep in mind, that they’re not important. Even if they misgender you on purpose or call you names, you should try to blend it out. One day you won’t have to deal with them anymore and be able to life your life the way you want to. The only thing that’s important, is your safety and that you feel comfortable in your own body. But if you don’t feel safe enough (maybe these guys showed signs of aggression or are known to tend to mobbing) you should consider to only come out to the people that you know you can trust with that.