I'm trying to lose weight/tone up and my mom doesn't help

I'm trying to lose a few pounds and tone my belly up before summer so I'll feel better about wearing a bikini, but my mom keeps buying and making unhealthy foods. She also won't let me start going to the gym to work on anything. I'm 16, 5'3, and about 140lbs. I'm not trying to lose a lot of weight. I just want to be able to look in the mirror and like myself more. I have some self-confidence, but wearing bikinis always makes me doubt myself. Since I still live with my mom, I can't buy all of my own meals. I can get a few healthier things for snacks and breakfast, but as far as dinner goes, it's either I eat it or I go hungry. What should I do?