You should not be holding or suddenly throwing your contact away to a jump. Get the impulsion you need in the corner, use your leg, hand and seat as needed to regulate the speed of needed but mostly focuse on maintaining the speed/rhythm and easing off the pressure once they listen, so that if you need to apply leg at the base, you still have aids left to add. Just before the jump, you can apply a little bit of leg but only if needed if they seem to be backing off.
I would advise getting a trainer.
Add leg 3 strides out and release them