The bottom part of you is missing in the vid!!
your back is not straight and tight when you get set - do that but keep the chest up. and your butt/hips shouldnt shoot up while your arms are NOT moving - they move in sync. I think if you fix that more weight is easy for you.
(once in a while I do that, lift hips - and my coach says 'hmmm... what lift is THAT you're doing?" I may name it. The back fly? the trap fling? gotta make it a good one!)