I'm not sure how old you are and what type of school you are going back to, but I think you will be fine. It sounds like the decision to return to school was yours. So be proud of that. If you are going back to school after a long absence, you're friends will be glad to see you again. Either way, let others help you. Don't be afraid to ask where to go, what you misses, or what has changed. Look at it as an adventure. You are going to meet new people, learn new things, and doing it for yourself.
On that first day back, wear your favorite outfit. It might sound silly, but if you are wearing something you like, you will feel more confident. Be pleasant and smile, others will return that behavior.