I think that you are obviously suffering from anxiety. First of all, you are a virgin, so of course you are nervous. Secondly, you are already thinking she may not be in to you - another very good reason to be anxious. Obviously the problem is not physical since you are able to have an erection when by yourself. You need to relax and get outside your own head. (no pun intended) This is a very common problem from what I've heard.