prom dress shopping

so i got my prom dress today and i absolutely LOVE it (which i never thought i’d say bc i usually hate wearing dresses) and now i’m feeling really bad and self conscious about it. it’s a little tight in the back and kinda shows how my tummy isn’t flat. what if it doesn’t fit in two weeks? i feel like i have to watch every single thing i eat and not gain any weight till after prom. help!!