How do I stay fit and healthy without school athletics and in a family that eats bad?

I'm a freshman in athletics and this is my first year ever being in athletics. I've looked at my schedule for next year and so far I haven't been approved to be in Athletics again. I can't really do much by myself because I'm bad at motivating myself, which is why being in athletics is a big help. I don't know what I'd do without athletics and I'm scared that I'm just gonna go back to the way I was before, not doing anything active and just being fat. Also, I eat as healthy as I can in school because they provide foods like broccoli, salad, wraps, corn, etc. When I get home, things change. My family aren't healthy eaters and when they provide the food, I have no other choice but to eat what they get. I really need help because my childhood has basically been ruined by the overweight kid I've been and I really want to change it.