Just do it. It's an experience everyone learning a language has to go through, I suppose. When I was studying abroad, I felt like an idiot more than once. After some time, I decided to ignore it, and I just opened my mouth and said something, even if I made a complete fool out of myself.
It helps if you're talking to people who know how you feel, because they have experienced it themselves when learning a language. They'll usually be more patient, and if there's some misunderstanding, they'll try to figure out what's wrong.
So don't fear :-) You won't learn it unless you practise, and that means making mistakes. Lots of them. That's just how it is.