Pressured for my 21st bday. Advice, anyone?

My sis and I are total opposites. Im the goody-goody studious one. She's the liberated party-girl. So my 21st bday is coming up and I feel a little pressured to do something with my friends, just because my sis always has something planned with her friends on her bday. She makes it seem like its a big deal and that I have to celebrate it. I dont feel like having some bash on my bday because I dont have as many friends). Im afraid that if I dont have anything planned, I'll seem like a loser. Thanks for the advice.