Is it legal for a school to punish you with manual labor? For example scraping gum off the ground after school or do they just have the right to have you clean what you did?

Schools have authority to impose reasonable disciplinary consequences for misconduct.  In-school detention, suspension and expulsion are the three most common types of disciplinary action.  But a school could require service work or mandatory Saturday school as alternatives.  If service work is required, the school may require the student to clean up more than just the mess that the student caused.  If a student refuses to perform service work, the school can resort to an out-of-school suspension.