How to boost my metabolism as a teen?

For some time I have been eating less than my body needs,so I guess my metabolism really went down =( I hated the canteen’s food and we weren’t alowed to have packed lunches so I just had breakfast,then I shared a choc bar with friends(they’re all hungry and I didnt want to be mean)and then I had a whole pack of biscuits or a chocolate waffle or something sweet from home,and dinner was light since my parents have light dinners.But then on weekends I ate enough,breakfast,snacks,lunch,dinner loads and loads!! But I guess my metabolism still slowed down since on the days of the week I didnt eat much(all of my calories still came from sweets and junk) AND I didnt get exercise AT ALL.I never was overweight but I’m heavier than most of my friends(they eat LOADS).How can I jump-start my metabolism and eat like all my friends,with ice-cream,chocolate…I seem to gain weight if I eat like them,now I can bring packed lunch to school but I’m scared I’ll gain weight cause my metabolism is slow!