Here, I hated PE too. Write down calories, and make up lame exercises to "burn them off" like running or swimming or dancing. Do it appropriately, sometimes you can't allways burn it off, like if you gained 100 calories and only burned 80. It's fine.
A rule of thumb is that about 100 calories per mile are burned for a 180-pound person and 65 calories per mile are burned for a 120-pound person. A 150-pound person will burn roughly 400 calories during an hour-long swim at a moderate pace and 700 at a vigorous one. The average person will burn 300-800 calories per hour dancing.