You are getting the stiff neck largely because you are shrugging your string arm shoulder up as you draw, bow shoulder is shrugged up a little too. You are doing what I call an "uphill" draw. Watch your string arm elbow as you draw. See how it moves in an upward direction? that is putting the bow weight on the top of your shoulders and your neck muscles rather than lower down on the back of the shoulder and across the back (trapezious and rhomboids).
Try lifting you hands together before you start to draw, relax and drop your shoulders down to where they stop and relax. Then move that elbow slightly downward as you draw and see how it engages the back more and takes strain off the neck muscles.
Actually a pretty good looking shot, but with a really good shot, you won't get a neck muscle pinch/strain.
Arne