The back doesn't merge. It looks like one of those copy/paste heads where the face is just left of there.
A trick would be to copy one half, and mirror the image, and just pasting it so the center part is on the outside edge.
That way, the center is in the middle, and working on it would be easier.
Eyes could definitely need more shading. They don't really have depth. You certainly did good shading on other parts, so it's strange how you skipped the eyes.