My hope is that the GM only has to play the gym staff and you guys actually interact in a semi free post environment. Leaving the time after and before school to free post what you do. Either family interaction, go to the arcade, have a romance, whatever you write will be what happens during your off campus time. This should allow for some creativity on your end and not feel cramped by the school scene. 

I would also allow for free posting during the lunch period where all student may interact on campus. It feels ambitious as I type it but I think it could work with your help.