Calida Response: This style you purchased is a low cut bikini. If you have a full bottom and need more coverage I would suggest Calida hipsters 21526 – mid cut or hipster style with coverage in the back. The fabric is a very fine pima cotton with a little elastin and they should not be moving around. Also, It sounds like you are not ordering the right size. I would suggest that you look at the sizing chart available just to be sure you are making the right purchase based off of your pant/slack size. Jane from Tarzana CA