I’ve had a fight with a friend and I don’t know how to fix it. Help!

First decide if you really want to fix the friendship or would rather it faded away. To fix it, spend a little more time together, ask the friend to your place, or hang out with them at school a bit more, and gradually you may find the friendship is back on. Sometimes it’s just time going past that heals a friendship.
Friendships can be up one week and down the next, or even on different days. If you need to apologise or ask for an apology, do that. And remember, you can’t fix a friendship by yourself. The other person has to want to, as well.
It can feel messy and upsetting, but sometimes you need to separate yourself from another person. One way to get through it is to keep reminding yourself what you want. This could be new friends who don’t tease you, or some other friends who do stuff instead of just sitting around being mean about other girls. Any sadness and stress you’re going through will be temporary, and your life will be so much better when you have drifted to another group or pal you feel more comfy with.
There’s more about how to drift away from a friendship and other stuff about friends in the book Girl Stuff 8–12: Your Real Guide to the Pre-Teen Years.