Your stirrups are much too short.
They are pushing you on top of your pony like a pea on top of an elephant.
Lower your stirrups, sink your weight onto your heels, anchor them at the girth. Now that you have a base from which to follow your horse, you can work on the rest of your position. Don't push off your toes. Relax your ankle and allow it to act as a shock absorber.
Allow your horses thrust to close your hip angle. You are extremely ahead of his motion, right out of the saddle as a matter of fact. Don't thrust forward with your seat. Remain in two point on approach, take off and landing. You do nothing. Let your cute pony do his job.
Because your too short stirrups are taking away your secure base, you are relying on your ponys mouth for support over the fence. Instead of pulling on his mouth to keep yourself from being left behind, press your hands halfway up his neck. This will offer you support as well as giving your pony freedom.
Release with your reins, not with your upper body. Hands go forward. Upper body does not. Your elbows are sticking out because they have no where else to go. You've ducked so close to your ponys neck, and you've brought your hands back so far, that your elbows naturally are squeezed out to the sides.