I made out and had sex for the first time about 4 months ago, all in the same night. It was quite intimidating, despite the fact that the girl isn't super hot or anything. Still, certainly cute enough to have had a bunch of experience and for the fear of that moment to linger in my head.
There were clear and very obvious signs she wanted to hook up, and I had already kissed her, so that wasn't an issue. The issue was that I didn't even know what to do with my tongue when making out and even though I had seen tons of porn, would I be awkward during sex? Well it turned out that making out was very easy, it just came naturally. While it was going on I had no problem making things more interesting by feeling her up and gradually getting off her clothes.
However, when it came time to do the deed, even though I didn't really feel awkward at all, I still had a lot of anxiety in my mind: would she find out that I'm new at this? Am I going to put the condom on wrong? Will I be able to last?
As much as I tried to suppress these questions, I was still nervous in the back of my mind. I couldn't get it up, at least for extended periods of time, and I couldn't get off even when she played with me. It may have been a disaster except for the fact that she really didn't care, she was just happy to be with me. Maybe I got lucky with such a nice girl, but I would imagine there are plenty of girls who are more than willing to be sensitive and take the time to make things right. Over time, things got easier and easier, and today I could balance on my penis during sex if I wanted to. She told me that no other guy did for her what I have sexually, and I think that's because we socially anxious types are generally more sensitive than most others. We care about other people and we want to please them. So we might hold ourselves back from time to time because of our extra sensitive emotions, but its better to start at that point and tone it down over time than to have no emotions whatsoever and just be a complete ****.
Anyways, there's really nothing to worry about. Just have fun, the less you worry the less there will be to actually worry about.