How to get belly flat?

2 weeks i am going to six flags white waters i went a couple of weeks ago but i dint like my bathing suit it was cute but i kinda of wanted to show my stomach and i live in georgia so its hot down south i do 5 sets of 50 sit ups every night i really don't see any major progress i just want to get my belly flat i do all-star cheer leading well i just started hopefully it will help