Can you do anything about a High School Band for cancelling a trip activity, but not giving your money back?

Yes. If the form stated specifically that the entire group would perform, all people who are not being allowed to perform and have chosen not to go should get their money back. When you signed the form, it was a legal agreement between the person and the school that they would take the person on this trip and they would perform, provided the paid the amount stated in said form. Make sure you have a copy of the form and ask the school board or contact the Board of Education. If all else fails, seek legal council.