Me and my new girlfriend tried to have sex and it didn't go well at all, I could only get my dick-semi hard and I feel like it would get a little softer every time is try to put it in so it wouldn't go in. Maybe it was just because it was my first time so I was really nervous or maybe it was because it was 1 AM on a school night and I was dead tired (I snuck over to see her).
Probably not the best circumstances to try for the first time. Don't sweat it though. Many guys have experienced a little bit of performance anxiety the first time. Just don't dwell on it. You will be fine.