I'm 21 and I've never had a girlfriend
Why have you never had a girlfriend?
I just prefer friendship don't want to have a relationship.  I'm not ugly or anything.
It's perfectly okay to not have a girlfriend if you don't want to. Lots of people don't seek out romance in their lives, so you can just concentrate on friendships if that is what is fulfilling for you.
My parents are not happy with this. They act like I'm a loser.
Your parents should not be treating you this way, so I hope that you are not taking their words to heart.  As long as you have good relationships with your friends, and are succeeding in other aspects of life, you are not a loser.  Don't feel forced into romance if you are not interested.