My point is that, in my experience, people are attracted to those who look like they are having fun. The hot guy/girl at a bar who is more focused on looking for the next person to approach than on interacting with others may look like a super model, but I'm not at all interested. The attractive guy/girl who is relaxing with their friends at a table full of laughter and exciting conversation, though? I'm all over that. You may be incredibly personable and fun to be around, but people aren't going to assume that unless they see it in action.
And, I speak from experience, here. As I hinted in an earlier post, I am super shy in situations where I don't know anyone. I tend to shut down, go quiet, and do my own thing. I still get approached in those situations by the icky guys looking to get laid, but that's it. When I'm out with my friends, though, and am confident and talkative within that group, I find that I/we tend to attract a lot more people -- as if people think that's a fun table, that's an interesting bunch, I want to be a part of it.
That's where the jump in and risk making an ass of yourself thing comes into play. Is it really that big of a deal if she wasn't looking at you? Introduce yourself anyway and go from there. Girls, unless they're unbelievably high maintenance and/or living in a fantasy world, aren't really expecting guys to be magically flawless. A bit of nervousness can in fact be quite endearing.