Hey girl!! Crazy, 'cause I was in the EXACT SAME situation a few years ago when I played volleyball in middle school!!
For right this second, all I'm gonna say is: DO IT!! :D
Girl, if you don't shoot this shot, you may never know if you would have been good or enjoyed the sport or not!! You should try!! What's the worst that could happen?? You get laughed at for trying?? Anyone with a brain would see that those laughing at you are total losers 
I did not get along the best with my volleyball team, 'cause, as you said, all the popular girls did it, and I was FAR from popular back then!! I also kinda sucked. Made my team very mad some days 
Gonna be totally honest with you, I just liked to travel, the sweatshirt, and the popularity that came from playing a sport XDXDXD
However, I made some AMAZING new friends by joining that team!! I also got to talk to some people that I normally wouldn't talk to, and that was nice sometimes :)
Sports tips?? Okay, um, here's a few things I learned from playing in middle school:
Well, know the rules, ofc. Don't touch the net with your body. Really learn if a ball is going out of bounds. Unless you KNOW it will be out of bounds, GO FOR IT!! :O Talk and communicate with your team while you're on the court and call the ball. Most of all, be kind and humble!! Be a cheerleader, too!! And PRACTICE PRACTICE PRACTICE!!
Good luck girl, I hope you do it!! Lmk how it goes!! :D
