This is what happens when you put all your eggs in one basket.
I am not saying you have to be a player, but you need to talk to lots of girls. Girls you find attractive, and girls that you don't. Truth is, you have no real clue about this girl's personality. You have a blank space, and you are filling it up with your fantasies. You want Little Miss Nice Butt to be kind and considerate. However, she might not be.
Or maybe she is. You'll never know unless you talk to her.
So, start small, and talk to people where the stakes are nowhere near as high. Get accustomed to breaking the ice and talking to people. You'll feel a LOT less like a dork and a loser.
BTW, if you feel that she somehow deserves someone else, who is smarter, handsomer, in better shape, a smoother talker, etc., then by not talking to her, that will become a self-fulfilling prophecy.
You never know until you try.