most of the time us guys are just as nervous as the girl. We worry about if we're doing this right or that right or am I big enough or whatever. Some worry can be a good thing as it can help build adrenaline but like pigglet said "the more you worry about it, the more akward it will become". In the heat of the moment you won't have to worry about if the guy thinks you're hot or not.. you'll be able to tell.. trust me
So no worries .. just go with the flow and when you do have it.. have fun