You've worked on so much stuff already, that I'd hate to mention it. But try to get your head into position and bring the arrow straight back to your anchor. I noticed that you settle your head into your anchor while or almost at full draw.
As far as the locked elbow, here is my advice, get your full hunting gear on and shoot. Your obviously not hitting your forarm now since I don't see an armguard or bruises. But that might change when you get some hunting clothes on.