Could just be normal anxiety; the thing to do for that is just enjoy being together and not build up the actual fucking into a huge issue. Practice deep breath, focusing your attention on other sexual/sensual experiences at that time--i.e. enjoy sucking and getting sucked, nip play, ball licking and caressing, talking sexy to one another. Even just mutual massage can be good!
Being open to one another about issue is probably good too. He may be feeling like he is not turning you on or is doing something wrong. So let him know that you want to experience this together, but that you are experiencing some performance anxiety. Make sex a playful experience, and just goes with what comes along. If you both are open to having fun together, and don't have a huge agenda of what needs to happen for it to be a good experience, it will be good no matter what actually takes place.
I have this acquaintance of mine that all our group has talked about. He has the scene so scripted in his mind, that if it deviates one little bit he can't get into the fun of it. He has had the opportunity to play with some great looking, really hot guys with great attitudes, but has stopped the action mid course because the guy wasn't saying exactly what he thought he should at the right time. Now there may be other issues, but it really seems to us that this is his issue--having too detailed of a script for play to go naturally.