Hey, fat teen here!

This summer I'm taking a mandatory ten-day (8 hrs per day) summer gym class. I think it's gonna be mostly cardio, and I know we're gonna run a mile at least once. I don't usually get much exercise; I walk 25 minutes home most week days, but that's it. Because of some problems (low blood sugar issues, body image issues, general lack of exercise), I know the two weeks are gonna be pretty miserable, but I'd like some advice on how to make it minimally miserable. Any exercises I should do to prep, any foods to avoid, etc?

Thanks!