I'd guess the height of the fence is about 2ft6 or so, looks like the height I jump with my friends cob!
Try not to get infront of the movement, wait to feel your horse take off underneath you :) what my trainer used to do was get us to look away from the fence so we would feel the movement. Bloody scary at first but after a bit you really click :)
When approaching the jump in trot, try sitting in the saddle 3/4 strides away. It helps drive your horse onto the fence. You seem to be folding to the side a little too, riding without stirrups really helps balance you up
Keep your weight down into those heels & it will stop your leg swinging back on the jump.
Good luck in the competition! Can't wait to see how you get on :)