There is actually nothing wrong with being that way. It's just the way you see it. I can give you my example, there was a time I used to live being an anti-social person. And I used to curse it the way you do at the moment. Nevertheless, I finally became more social. Had a whole lot of friends. We used to hang out, enjoy and had a lot of fun. And then today when I look back at the time when I was anti-social, I miss those days.
Believe me, your friends will change you. I always used to think that atleast my friends weren't the kind I could say would do peer pressure and accept me the way I was. They probably did it inadvertantly, but I find myself more and more like them. If you ask me, most friends would do stuff so that you lose your identity, what sets you apart from the rest of the crowd.
Most anti-social people are those who think out of the box, they have different views on everything. Most of the time, this difference is what makes you more respectable later, you do great things because you are just not anyone else.
One day, just don't do what you would do usually. Just sit back and relax, spend the time in solitude. It ain't gonna hurt you. Don't push yourself to do something that you are not meant to do. And believe me the feeling of being left out, being lonely, if you change it to solitude, you'd love it much more. I ask you no more that to just try it for one day, don't take your loneliness as a curse, call it love of being solitary. If you won't feel left out, you'd love yourself much more.