Confidence knows many forms and methods of delivery. Sadly, the most common form is that of the drunken idiot who really has nothing to be confident about that means anything. But he puts on a good show.
Build a base for yourself so that you can be confident, and have a sense of humor. Don't be clingy or needy. Tease her and make her laugh. Be interesting and possess a breadth of knowledge, and pursue a breadth of experiences. This will add to your life, and also give you things to talk about and stories to tell. 'Social Capital'.
I don't drink, and I don't party. But I have a girlfriend who I've been with for a number of months now, and I believe that if I pursued the matter I could probably date this girl that sits next to me in A&P who I sort of started talking to/flirting with for practice.
"Hello, fine lady. I see you have noticed my monocle, and my dashing top hat. Very good.
Now, pray tell, would you like to see my trouser snake? Because he's right down here, and he wishes his presence to be known."
Like that?