then you need to work on your self esteem.
have a few drinks first, then you wont worry as much, thats a scientific fact. then once youve ''approached'' a girl and found out that they're people 2........ur confidence will grow and eventually you'll reach the point where you no longer need drinks 2 approach a girl, and ur self esteem & confidence iwll grow, and u wont be as scared of rejection anymore
orrrrrr you could continue to hide in a cocoon your whole life and sing along to what about me, coz ur 'such a nice guy' but 'none of the girls will talk to me' ------ a lot of the time the girls are waiting 4 u 2 approach them, and if u dont they'll think u dont like their looks or something, and then walk away
i suggest u just down a few beers, go up and approach the girl - in a non stalkerish way - and just stop worrying, have a good time
u might be surprised with what you find.