While I'm riding my legs are still, and I have a great seat, but I can't seem to keep my hand completely still while riding my jumper collected, do you have any idea of where it comes from and how can I fix it?

Relax your shoulders! Your hands are probably not moving because shoulders get tense when you are working out.
I would say as long as you aren't nocking him/her in the mouth or anything then your hands don't have to be completely still. Let your hands move with your horse (extending from the shoulders/elbows) and that will allow you to maintain the same amount of contact on the bit as well.
Join the fun and sign up to connect with our 200,000 members!