I'm Soooo nervous about swimming with my boyfriend and his best friend?

They both go jogging and swimming together on a regular basis so they spend a lot of time together. And well...she's a lot prettier than me. I asked my bf if I could join them when they went swimming. Without thinking about it he said yes. But now I'm so nervous because I have to be in a swimsuit next to his best friend. She has a muck nicer body than I do and I'm so jealous of her. I'm so nervous about this what do I do?