I'm in so much trouble! Please help me!?

[Zoe]

Oh dear!
you are in quite a situation
well lets see what can be done.

Firstly, its clear that your friends are not very nice people. You should talk to your parents and be honest with them, and ask for an apology. An apology can take you very far. Accept that you were at fault and you will never repeat such behaviour and that you did not realise that you were being so mean, cause you thought it was harmless, since you weren't saying anything to Clair (to her face).
This might help you strengthen your case.

Don't worry you will not be expelled from school. This is all scam to make you bad. So relax my dear.

Lastly, at the meeting do not talk back, at all!!! stay calm and keep apologising and admitting your fault.