Hi =) I was in the same situation when I was 18, once again when I was 19.
First boyfriend I dated was terrible: When I was 18, I got my first boyfriend. I was very very anxious, so nervous, it was terrible. I overthought everything I said, I freaked out when there was silence, I never show3ed physical affection because I was nervous. I think everything I could think of that went wrong, did go wrong. I freaked out about it going wrong, and I propelled the relationship to a fast death. I cried everyday for the 4 months we were together.
Fear not, young one =p It was a learning experience! The thing is, that guy and I never really clicked, he didn't understand my point of view, and I didn't get him (he was very social, always wanting to party, etc.) and I loved staying at home to write, or write songs, and just chat. I was convinced that the reason why the first rel was terrible was because of personality differences.
But I'm with my second boyfriend for more than 1.5 years now. First date, I was nervous as hell. For the first 2 months, I was exactly like I was when I was 18, I freaked out, I thought everything was going to end, so I was just a terror. But I dunno, this guy, unlike the first guy, was so kind about it all. I would confide in him about my fears (like I was scared he was using me fordating experience, etc.), but he just reassured me all the time. And this takes me to where I am now with him.
I think I realised that there's nothing such as 'screwing up' a relationship/date if you really cared about it and the guy. It's about him and you earning each other's trust. So if they bail based on one bad date or something, that just shows he won't be right for you.