TeenHelp - Worried about college and relapsing

I've been experimenting since I was 12 years old with Alcohol and I eventually moved on to over the counter pills at 13-14ish. I don't know if it's addiction but at my lowest point I would only care about my next fix from drugs or alcohol even if it meant doing it at high school. Seriously I don't know how my teachers didn't realize I was high and spaced out O.o anyways I decided to get clean at 16 and it was pretty much on my own and I did it by using all the drugs in the house and not buying anymore. It was SO HARD for a LONGEST TIME. Sometimes I would literally fast walk out of the store to keep myself from buying anything :/
Well anyways I'm SUPER worried that once I get into the college scene that I'll fall into my addiction again because a lot of them like to use drugs and drink alcohol. Help?! Oh btw I'm not going into college until September 2013 since I took a year off after graduation.
I forgot to add that I've been craving drugs and alcohol for a yearish so I'm worried that'll make me vulnerable to start using as soon as I get the chance and I'm also paranoid that if I were drunk and offered any drugs regardless of what they are I'd say yes.