Can someone make me an outfit for a swim party?

So I'm going to a swim party this week and I don't know what to wear. Its going to be like 90 degrees and its so hard to choose what to wear because I wanna be casual but trendy and be able to impress everyone who's there. I also need shoes and a bathing suit so if u guys could add that in. Also I'm only a preteen but I dress in juniors or like older kids stufff. Thx guys