Okay I'm going to take a crack at it!
First off you need to shorten your stirrups, they are too long for jumping. Your stirrup also needs to be moved closer to your toe to allow you to flex in your heels more. I think you ride a little bit hunched over, but it may just be the jacket. When you go over the jump, your knee pinches and your calf slides back and your heel goes up, which causes you to tip forward at your horse. If your pony stumbles you could easily go off over his shoulder. Most of the jumps you are back in the saddle too early, mostly because you're not holding yourself with your legs and core.
To improve all of this, make sure you have a solid
jumping positions/two point at walk, trot, and canter. Do no stirrup work (like you already are doing) and make sure you shorten those stirrups! You may want to jump some smaller things while you improve your position. Do some leg and core strengthening exercises off the horse to improve strength and balance.
Your pony is really cute by the way!