First of all, you are still young, so you don't have to care too much about your health. Study hard, there is plenty of time to make you slim when you go to college.

To lose weight, sit-ups can thin your stomach.

But the faster and more effective way is: "Lie flat, with your legs and head slightly raised by about 30 degrees, and stick to it for as long as possible. Stick to it for 20 minutes every day, and you will have thin legs and a small belly. Much more effective than sit-ups. The method taught by my former aerobics teacher is quite effective.

Moderate exercise and eating less and more meals are the most scientific.

Swim more if you can.