While I agree with most of what PumpkinzMyBaby22 said, I'll have to disagree with the part about the release. You don't have much of a release at all, it seems like you're keeping your hands planted to the neck and leaning forward over the jump. Think about moving your hands with the motion of the neck, grab mane a few inches up the beck before the jump, if it helps. Practice two-point at the walk, trot and canter with your hands out to the side (safest to do this on a lesson horse on the lungeline) and practice on keeping your legs still and forward. This will help with the problem you have with them slipping back. You can practice this over poles and little crossrails, too. Also, try counting aloud "3, 2, 1, JUMP," so you don't get ahead of the horse. I also found that counting a rhythm aloud "1,2,1,2" helps with keeping me waiting for the horse to jump, rather than strain to jump ahead for the horse.
“Have fun - Stay on top.”
"There's nothing like sixteen hands between your legs"