How many crunches to do a night to get a flat tummy?

I’m 15 and eat right mostly lol. But how many crunches would you have to do a night to get a super flat tummy? Just think some improvement could do some good. Any suggestions on how many to do? I used to try 300 a night but than i lowered it to 200 because I also go to a gym after school 5 days a week. Just wondering? Hope you can fill me in! :)