Sorry I didn't reply sooner.
Even though you're in school during the day doesn't mean you have limited exercise time OR can't eat healthy. How come taking your lunch to school is not an option? Most schools these days follow strict dietary guidelines and although I'm not sure what your school is preparing, you could find something that is healthy! My old High School had a salad bar, chicken fingers & fries line, Subway, regular school food, and homemade pizza line. I'm sure there's some sort of variety at your school. If not, I highly recommend you taking your lunch to school so you know exactly what you're eating & what is in it, therefore you can monitor closely!
Also, say you get home from school and have homework. Do your homework first, then go on a walk/jog for about 30 minutes, ride a bicycle, do jumping jacks and/or push-ups/sit-ups, swimming, or something else that's active! Any activity that keeps your heart rate up for at least 30 minutes about 3-4 days per week will help with your weight loss; it could be anything you enjoy doing or the few I've named! But, in order to lose the weight, you have to be dedicated & not make excuses as to why you're not eating healthy or exercising