Congrats man! You are now officially a bad a$$! You seem to be on the right track now... Keep on having sex with her though because you'll get more experienced and confident. Your also lucky she has friends; you might be able to hook up with them too. Also, she wouldn't keep having sex with you if she didn't like you.
If you've never had problems with getting a hard on before, than it's obviously a mental thing. You have to just forget what happened the first night and completely erase it from your mind.