Is it rude not to eat at the breakfast buffet at school?

Tomorrow we're having a buffet with the class, and I'm afraid it'll be rude if I don't eat anything. I have an eating disorder, which makes me really uncomfortable eating in front of others. Plus, I don't know anyone in my class and don't have any real contact with anyone.

My teacher is very strict about this and forces everyone to participate in class activities. I'm afraid it will look like I was too stupid to remember to bring plates and cutlery, and that it will come across as if I'm just using it as an excuse. I really don't have a good relationship with my teacher, and I'm also afraid of myself.

Do you think I just can't eat anything, and what should I say if she gives me a hard time about it? 🙁