First off, how old are you and when you say going out, do you mean boyfriend/girlfriend or dating?
The truth is, if a girl was really feeling you, she'd be the happiest girl in the world to get a kiss by you. Imagine all those teenyboppers who would get a kiss blown to them from some casual boyband. They'd go crazy.
If you displayed a confident, masculine image of a man who knows what he wants and takes it, then you shouldn't really have a problem getting physical.
I think this is what happened. You asked her to be your girlfriend before you ever kissed her to judge her interest level. If this is the case, then you're in for a shot down in the long run. Of course there is a possibilty that she is REALLY interested in you, but the only way to tell that is through the first kiss, BEFORE the relationship.
Think about this. Say you were a SHY guy, but you had wants just like everyone else. You like getting intimate with your special someone, which every person in a relationship should, and you date a super cool girl who you are totally digging and she is totally digging you. Would you get uncomfortable when you're alone with her? You shouldn't be, you're dating her, you know she likes you and you like her, no matter who she is.
There is no way to control her level of comfort. What you CAN do is control yourself and what you do. There are plenty of odds that can say she doesn't even like you, but you didn't leave much info, so she possibly does. If you played your cards right, your girl should be trying to jump on you every chance you get.
Quit worrying about her comfort for a while. You want to kiss her, so kiss her, you want to make out while alone with her, make out while alone with her. Girls WANT to be lead. They don't WANT to give permission. They WANT to be seduced. It takes a MAN to fufill what they want.
When I was younger, I would always worry about how my girlfriend felt, if she was uncomfortable, if she still wanted to make out, if she liked what we did and I would question her. That makes you come off as annoying and unsure of the situation. Everybody wants someone else to lead them, it makes them feel protected and in turn it makes them more secure about the situation. Quit worrying about how she feels, do it because it feels right for you. If it doesn't feel right for her, then I'm sorry, but it isn't going to work out.
No experience doesn't matter. If she likes you, then she should want to experience things with you. If your GIRLFRIEND is uncomfortable around you alone then you shouldn't be in the position to call her that.