Birthday Party RSVP Help, Please read?

Okay, so right before spring break I gave out invitations for my 16th birthday party, I put an RSVP date on the invitation and included a phone number and e-mail address. Not very many people have gotten back to me and the party is in about a week. I need to know about how many people are coming so I can get enough food and soda and stuff. (Plus some of my friends are vegetarian/have dietary restrictions and I nedd to know if I need to have special food options for them.) I'm not sure if people have just forgotten/misplaced the invitations. Is it rude to ask people who have not responded if they are coming or not? And any help on how to ask without being rude?