This is a very common problem on here, and you need to know that you are not alone. As to an actual response to your post, the first thing that I will say is this: There is nothing that you cannot change.
I used to be in a very similar situation to you, I always felt that I wasn't as good as everyone else, or that, maybe, I wasn't trying as hard as I could do. I felt this way because I was in a selective school, and so there was always someone better at anything that I would try and do.
The changing point in my life was getting a job. It was in a pub, so forced me into the social situations, and I had the knowledge that, if I didn't push on through with it, I both, wouldn't get paid and would be letting other people down. This is what gave me the experience that I needed to become more confident in my own abilities, and to be able to get out and enjoy myself.
Another thing I can recommend is to join either a public speaking society, or an amateur dramatics society, because, while both require you to speak to people, they also give you scripts. You know what to say, and you know that what you are saying is correct, which is a sort of safety net, making sure that you have something to say.
Overall, I would say that, while you can change anything about yourself, it is you, and only you that can take the first step. You just need to build up the confidence to do it.
And now to end the speech with my customary Monty Python quote:
"You'll see it's all a show, just keep 'em laughing as you go, just remember that the last laugh is on you!"