I don't know what's with people here giving the crappy advise that you should "go here" and "smile there" and "be this" and "do this there."
That type of advise is exactly what's making you so hesitant to just go out there and be who you want to be and do what you want to do. If you force yourself to do something because you feel like you should, then that probably won't sufficiently cure your unhappiness. You'll be living your life based on someone else's set of rules instead of your own.
It's okay to be quiet. It's okay to feel unsure, and scared, and intimidated, and nervous, and shy. There's nothing wrong with those feelings because that's just the place you are now in your life. It sucks, it really does. It's a pain in the ass, and it's scary as hell. But it is the way it is, y'know?
Accept who you are--don't bully yourself or put yourself down for not being something you're currently not. Accept all your feelings, even the negative ones. They are only your mind's reminder that something needs to change in your life--they're fuel for your fire.
Here's my advise:
Try not to feel like you have to talk to or smile at people. But try and recognize what you want to do, and then try to figure out what's stopping you from doing the things you want to do.
I think the only reason you're hesitating is because of your fear of social interaction--you're afraid that you'll do something "wrong," or won't do something that other people have said you "should" do. And hey, this fear is perfectly understandable. You're not used to being around strangers. It's the unknown, and we're all inherently afraid of the unknown as a survival skill.
Just try and tell yourself every day that there is nothing you should or should not do. You write your own rules. If you don't feel like being sociable, then don't--just walk in that building, ask for an application, fill the sucker out, and hand it over. Yes, you'll probably feel insecure and way out of your element, and that's fine. You're going to feel like the world you're so familiar with is shattering, and that's fine.
Just try and not let these feelings overwhelm and control your life any longer.
Eventually, if you keep pressing on, those feelings will dissipate and finally disappear. And you will feel incredibly strong, especially for making it all that way on your own terms, blazing your own path.
I'm going through the same exact thing you're going through now, and man, I feel really dumb too. But you're not dumb. We're not dumb. We're in a shitty place right now, but if we grit our teeth and start the painful ascent, we will get there. We're going to slip and fall, and we're going to feel like it's not worth it. But if we keep climbing, we will arrive at the destination we want to reach. And I guarantee you that there will be thousands more below us, hesitating like we did before, and we will reassure and encourage them.
It's all easier said than done, but it'll be fine. Take each day at a time, even if you're scared shitless.
I hope this post makes sense!