You鍊體育,so you will not fat if you don't eat after doing exercise.You said that your weight have increase 3 kg,but your BMI is only 20,it is a bit thiner.
If you still think 自己快變成真正的胖子惹 ,you should eat 3 times a day.You should eat more vegetables and less meat.
(Your 大腿和小腿 is 很粗,I think it is not fat.)