Unfortunately mate theres a fine line between being 'cool' and seeming disinterested...though both do work!
If she thinks that you are a strong person that can stand on your own two feet without the help of anyone else, then she's gonna want to be around you. As soon as she thinks that you need other people, ie her to be the person that you claim to be, she is very likely to loose interest completely!
I know because this is me! All my life i've wanted/needed a girlfriend by my side to cherish and have fun with, and because I wanted this so badly for so long, I was giving off really bad vibes to the girls I was attracted to because I was so nervous! Now that I have more of a sense of who I am and where I want to be, I have found that I am not as attatched to the outcome of every situation, because i am confident that i will eventually get there.
I guess the key is to look at the bigger picture and see that either way, whether you hook up with this girl or not, theres a shit load of other women out there and you've got plenty of time (hopefully) to go out and meet them so what the hell there is no rush!