I think the others said it for the most part.
With a jump of that size, and being an oxer, I would've given more on the release, so the horse wouldn't look as stretched out as he does. A longer release would've allowed him to use and round his back more. Instead he has to go more for a reach approach due to the restriction on the reins.
Also, you are a little behind the center. Which is also affecting his jump.
Your hunched over him, I'd suggest really work on pressing your shoulder blades together and opening up your chest. Your back should be flat, and although yours is to an extent here, due to the rounding of your shoulders, I can only imagine what the landing looked like. Your shoulders hunched over the jump is going to make you majorly slump into the saddle on the landing, even though you may not feel it. (Trust me, I had major issues with this with having scoliosis!)
Try riding with a back-brace during training. Nothing fancy, just something to help you train your shoulder muscles and train your back to "arch". A good solid position over a jump could also majorly help you with your release, you'll feel a lot more stable in your own seat and feel like you won't need the reins as much for balance.
Your legs look good, do you do no-stirrup work? I'd suggest doing some (Although I'm sure you probably already do :) ) just because your toe does point out a little. Although I know that is the trend in most of the Hunter world, it can lead to pinching with the knee and many other issues, so just be sure to keep an eye on it.
(I toe out too, so I do lots of no-stirrup work as well! :))
I love how your leg, even over the jump, still draws a straight line from your hip to your heel. I am assuming it does on the flat as well, which would mean since you are able to keep the position over the jump that you do have nice solid legs.
Your horse is VERY cute and has a very nice expression. Even though he is restricted by your hands, seat, and body, he still has his full attention back on you and is truely trying his best, and despite that he is still looking really good in the front end.
His right knee is more loose than his left, not quite as tucked, but I am sure once your position is corrected, he will tuck his knees evenly and round out more. He looks like a very scopey jumper and you both are very well turned out!
VERY cute horse! The braiding looks very nice as well!