PLEASE don't worry!! Everyone feels like this, and most are only drinking because it makes socialising initially so much easily. You WILL make amazing friends, but it takes a bit of time. You'll make pals through sharing experiences on the course, not necessarily how drunk you get in Freshers week. If i recall, most of my friends I didn't even meet in Freshers week, and everyone went around with completely different people initially than when the course got underway! Keep being smiley and nice and interested in other people- ask them questions, everyone likes that! And it means you can listen and nod and make friends that way. You will open up, but you are just a bit more reserved, that's all. I'm the same.
Stick with it- real friends take time to make and maintain. Do have a drink and go to all the events, even if you don't feel like it, and just try and have fun- that's why you're there. But do be assured that everyone is feeling as anxious as you, and missing home, but they are just covering it up!