[Bigwill]

When I try to keep the right wrist bent back my left wrist doesn't uncock for some reason.

You may be preventing your right arm from straightening while you're trying to keep the right wrist bent. I know that I've had that issue before. If you allow the right arm to extend (w/o flattening the right wrist), the left wrist should uncock, since it is the bending of the right elbow that should cock the left wrist in the first place.