How old are you? If you're still in highschool, talk more in class. Now, I'm not talking about chatting to your neighbour, but join in any discussions. If you have a group project, take the lead and talk to everyone. You feel like you're antisocial but you just don't have good social skills is all. Entertaining people is not easy or a skill everyone has, public speaking is not a skill everyone has, but you can work on them. I found as I participated more in highschool, I became more confident. Most of the people were my friends, but some people I rarely talked to, so it was sometimes nerve-wracking being in a group of 5 people and I don't say more than a hello to each of them everyday. Have fun with stuff like that and you'll find your groove.
Some of my buddies aren't necessarily antisocial. My friends and I were talking to these girls, and they were pretty hot. My one friend who I'll call Ace, isn't the most social person. He's not shy, but he usually talks the least out of any in our group if we're around strangers. Now, he probably hit it off the best with these girls since he would always choose what he said wisely, and came in with jokes and interesting comments. I talked my ass off, and probably blew it with all of them (not that we even got any of their numbers, but if we tried, I'm sure they'd say "Yeah, give us all your numbers, oh but not you, we don't need it."), and he came in here and there and totally charmed them.
Maybe you're not going to be the main act when chatting with girls, maybe you're more of a sniper and come in here or there, you don't really know yet and I think that that's you're problem. You're not antisocial, you just don't know your own strengths and you haven't honed your abilities.