I'm an inch shorter than you but I'm 10 lbs heavier.
It's not that big of a problem though. It really depends on whether you want the ball or not. I was usually the smallest big on the floor when I played, but I made sure that if I couldn't get the ball, I'd make my opponent work hard to grab the rebound. Nothing wrong with getting a bit bigger and gaining muscle though. It'll actually help get through to the psyche of your opponent. If they see that they're at a disadvantage physically, the pressure they created for themselves will kind of break them down a li'l bit. You shouldn't just train for mass though, as I think someone earlier said. You should try to find a balance between training for mass and training for strength. I've found resistance bands really helpful. I mean, I've gained 10 lbs since using them (most of it muscle) and I do feel stronger and more durable (? - can't think of another word as of the moment
). Well, the real test of that would definitely be when I start lifting (which I'm also trying to start. Looking around for a walk-in gym), but then the resistance bands have helped me a great deal. I'm not the biggest person of authority on this type of thing, but I hope this helps in some way!