Food help asap ! please :)?

hey, im 13 and kinda tallish i hve an alright figure abit of astomach but close to a flat stomach , the thing is i eat healthy for atleast a month i tried to get my flt stomach but healthy eating didnt do anything, so i gave up and starting to eat a bit more junkfood i still eat me vegies and fruit but im eating junkfood aswell its been 2 days since ive started the junkfood i feel the same so is it okay to eat a few chocolates and chips a day ? and i only do netball on tuesdays and saturdays so it that enough for me to eat junkfood then i can just work it off from netball or i need to do more sport?