Okay so my computer is a bumfluff so I can only go by what I see in the pics, can't comment on the videos cause I can't watch them.
You lower leg is very unstable and it looks like your throwing yourself at the jump (I find that once you sort one out the other usualy comes right.)
I would suggest lots and lots of riding in a correct two point position, I personaly spend 15mins of every ride in two point, It will get your heel down and your calf agianst the horse in the position that your leg is the most effective.
Try riding around in two point concentraiting on your weight sinking through your heels with the front of your toe inline with the front of your girth and your toe turned slightly out, have a straight line shoulder knee toe and push your bottom towards the cantle. Do this in walk, trot and canter, change gaits and changes within gates (collected, medium etc) on striaght and do things like serpentines and other schooling excersises. Once you can do that being stable and your lower leg solid agianst your horse then bring in trot poles raised trot poles and little jumps and go in in your two point and just ride through, you dont need to change anything just concentrate on your position staying still and you will be fine.
Good luck with your show, your horse looks like a real trooper =]