Since you scanned a Don Post, you really should check with RotJ reference. But what I can see right off the bat is that you need to straighten out the curvature on the right side of the neck - left in the picture - to be more soft curved like the left side. It should not stick out so much down at the bottom. The top edge of the chin vent should probably also be straightened out a bit, as it shouldn't curve at all.
Also bear in mind that screen shots from the movie has warping due to the camera lens, distance and zoom.