Swimsuits... I have no boobs

I bought these two swim suits and I'm trying to decide which one to keep. The red and white striped one looks best because it covers my back fat and thunder thighs, lol. Plus the low cut one doesn't look great because I literally have no boobs to keep the top in place. Why do I have no boobs? Which one would you pick? (EDIT: I tried them on with my underwear on so there's no reason to not return them. Doesn't everyone try on swim suits with your underwear on?)