Often whenever I try to approach a girl, especially some girl who looks slightly older than me (I'm 20), this thought creeps in my head that I have no business talking to her - more specifically it's like I just don't see how a girl would ever be able to look at me in a sexual manner, even when I think I look good. It's just a completely foreign concept to me that an attractive, bitchy-looking, young, female stranger would want to fuck me, or that I could make her want to fuck me...sometimes I forget I even have a dick and there are times where I'll approach a girl and my voice comes out sounding like a little boy's which only reinforces my self-image of not being sex-worthy..how do I get over this?

Edit: I look fine, I'm not short and can often look quite masculine, but it's like I don't fully trust that I'm the compliment to a woman when half the time they act like they hate men.