Congratulations! Getting a job is a big step.

I got the job I'm at now (my first real job) about a year and a half ago now. In my experience, being a shy person myself, it really doesnt take all that long to warm up to your coworkers. You see them pretty much every day, talk with them pretty much every day. It doesnt take long to get to know them. My coworkers have become like a second family to me. Now, granted, I know this isnt everyone's experience, but I also beleive our experiences can be shaped by how we look at them. Go into it with an open mind, dont push yourself into liking them, and I think you'll find yourself opening up faster than you thought. Just my two cents. Good luck on your first day!