You're literally laying on your horse's neck and are in front of the pommel. You want your center of gravity to be with the horse's, not in front of it. If your horse had stopped or ducked at the jump, you probably would've gone flying
. It looks like (but the pictures are blurry so I can't tell 100%) that your toes are turned out. That creates a pinching with the back of your calves. While you don't want to force your toes to point forward (that could create pinching with your knees), you want to try to keep the sides of your calves softly against the saddle flaps. Lastly, your back is hollow, work on keeping it flat. That will be easier once you're able to jump with your horse instead of in front of him.
Good job on keeping your head up and looking forward
! That's one of the hardest things to do since it's instinctive to look down. Your horse has nice form, but seems to be jumping flat in a few of the pictures. This could be because the jumps aren't challenging enough for him, or because he's trying to compensate for your center of gravity being in front of his (or a combo of both).