I respectfully disagree with Creeker.
As an 18 year old, I think you are showing maturity and good judgment by choosing not to drink despite the fact that your peers are consuming alcohol.
It is difficult for a young person to find any social events where no has consumed or is consuming alcohol. It doesn't seem reasonable that a young person should have to avoid any friends who drink as well as avoid going to any social events where there is alcohol available.
I would say you are fine with what you are doing. Don't drink, don't get in the car with anyone who has been drinking, and if the cops show up to a party you are attending don't do anything stupid.
Cogito ergo summopere periculosus.
Fiat justitia, ruat coelum.