Your'e too young to not be doing anything fun, cool. I'm sure your friends are doing something. Don't worry when you get my age (35), and your married with a 16 year old stepson it doesn't get anymore boring. My Friday nights usually consist of Food Shopping. In fact , I'll be doing it whithin the next hour.
If it makes you feel any better, I'm not really doing anything tonight either. Trying out a new online game, my girlfriend is up in Boston, otherwise I'd be spending tonight with her, so you're not the only one without a life this weekend.
If its bothering you though, go out and find people. Join a pickup sports group, a club, heck to just go driving and explore a part of the region you live in that you've never bothered to before. If you're over 21, head to a new bar, be as friendly as possible. Worst that can happen is that you get weird looks from a bunch of new people, and can just leave the bar and never worry about what they thought of you anyway, best that can happen is you make some new friends, maybe meet some women, and have a good time.
Either way, its the weekend, and you should take advantage of it to do something you'll enjoy, whatever that may be.
I'm actually a little jealous of you! I have a full weekend - busy tonight, Saturday morning, afternoon and evening, Sunday morning and evening, and if I'm lucky I'll get to sandwich some time in there Sunday afternoon to mow my lawn which has taken off like crazy.
I'm looking forward to Monday morning already so I can rest here at my desk again!