It's hard enough to make friends in a school environment anyway, let alone with someone making it even more difficult for you. This other girl is a bully, she is making your life difficult and that is bullying. She's trying to turn everyone against you. There is a simple way of getting passed this. You need to show all those other girls the kind of person you are. You need to show them that you are not that bad and all of the things this Sam person is saying about you are lies. Poisonous lies.
You could always approach this other girl and ask her why she is treating you like this. Ask her why she is attempting to make your life a misery.
Alternatively you could try making friends with the guys instead. I've always found it much easier making friends with boys anyway.
I wish you the best of luck and hope that this all works out ok.
-Cara