I don't see what is so confusing, but follow this advice:
Sit back, relax. Don't see everything as fight, or you'll spend your entire life making enemies when what you really need to make is friends. If someone judges you unfairly, big freaking deal, it's their problem and it won't affect you in the least unless you make it YOUR problem. Sure, some teachers aren't fair, but you need to deal with that, too; everyone does, and you don't see the rest of us getting kicked out of 6 or 7 schools. Lastly, just because someone else is bothering you, it doesn't mean you need to pick a fight with them; observe, stay calm, and learn from the situtation WITHOUT losing your nerve and mouthing off. Stick to your guns when you absolutely need to... but when you don't (and in this case, you DEFINITELY didn't need to - it would have been in your best interest to have stayed seated with your mouth CLOSED), it's okay to fold, to say you are wrong even if you don't think you are. It won't hurt you in the least.