Im seeing 2 things
1 you could add some more edge to help slice the bow down.
2 you're rocking your body back and forth... concentrate on lifting the bow up with your knees and driving the bow through
have you tried to do this on the move... get some forward momentum then do the double pump.... rmemeber to not lean back but twist your body up then release. looking over your shoulder (where the head goes the body will follow)
btwthanks for posting a video link...it is sooo much more helpful to see it then give bland answers