Am having sex with my girl and she remains still its the 1st time we had sex could it be that i was not just as good as her ex ?

You should ask: She's the only one who can tell you what is going on. Sex is a sensitive issue, so try to pick a time to talk about it in private before you attempt it again. Try something like, "say it didn't seem like you were enjoying yourself last time, what can I do differently? " and then make sure you understand what she wants. Then you can let her know what you want. Communication is important.

Communicate: Communication is very important -- finding out what likes and dislikes are will help you make the times more enjoyable. You're the only one who can communicate with your gf. Good luck!