My favorite thing about friendship is that they make fun of you. Which sounds weird, but when people are polite it seems fake and like they don't care at all. Maybe those kids don't care about you at all, and if they do, the bast thing to do is turn the other way. Not literally, I mean stop hanging out with them.
Also, you can try defeating the ender dragon in full survival, to show them you actually aren't a noob. It's actually pretty easy to do it too, and it only takes like 2 hours or less. That way, you can tell them your not a noob, and they might start caring. If they're good friends.
If you need help learning how to plan for the ender dragon fight, I can help.
Also,it is a bad idea to tell the principal. Doing so will make everybody make fun of you, and will not help the situation. The best thing to do is think of a passive comeback to any and all of their comments. What I do is make a joke about how bad I am at minecraft to show them I don't care what they say about me. And also, they might laugh which probably means they might be friendly, or the total opposite, depending on the kind of laugh