Aerobic exercise can reduce fat, but it takes a long time to exercise. The pound you lost is probably the weight of water. Maybe you eat more carbohydrates when you go home, which leads to fat accumulation. After water supplement, you will gain weight.
So be sure to replenish water before exercise, and don't drink water after exercise. Eat more foods rich in cellulose and control the intake of carbohydrates (that is, staple foods).