For health it is not important to eat too much.
You should take balance diet.
Where carbohydrate, fat, protein, vitamin, mineral & water should be present. Your sleep, exercise, cleanliness & prayers & good behaviour with everyone do count a lot.
Take care of your teeth as well. (Better to brush them twice a day or after every meal). Whatever you eat you must digest it by physical activity. Act upon this plan inshallah you will be the healthy boy in the class.