I'm really self conciuos about being seen by guys in a swimmin costume,...?

You are who you are and you have the body you have. You won't become Kate Moss in a week. The best thing you can do is just go and have fun. If you want to work on your body, that is great, but don't expect extreme results in a week. Just wear a bathing suit you think flatters your body and get out there and have a good time.