Broke My Arms 7 Years Ago, But Never Set Right?

I am 15 now and I broke my arm when I was 8 actually it was the growth plate on my elbow, and I never had surgery on it, all I did was have it set a the hospital and a full cast put on for 5 weeks. Anyways I was exposed to do occupational therapy which i did for a few weeks, but after that I was exposed to do exercises that made my arm turn better, but I didn't. Now all these years later the farthest I can twist my arm is a little further then when you go to shake some ones hand, I (can) move my arm a little past that point, but can't give some one a low five. Any ideas on what I should do, and in fact my arms seems like it used to twist further when I was younger, is this because I have been lifting weights and working out?