Oh, very nice! My suggestions for fixing it up are to hard to describe, I'll use an edit this time.

So, you were right about the shadows not being as dark as the reference, so I added a new shade, then took everything on the shaded part and shifted it one step darker. I changed the curve of the ridge to better match the reference, with a less shallow curve and more room for the forehead. The top's shadows were hard to pinpoint if you just go by the reference image, but that's where real world knowledge is helpful. It's mostly a ball shape, and if you light a ball from that direction, you'll get more of a swoosh than a circle, and if you know that you can see it in the reference. I removed a few spots of what I guess is reflected light along the outline, as it was in places where there wouldn't be any reflected light. I did, however, add a bit of extra highlights on a few edges. This isn't reflected light, it's ridge lighting, it's a way of making a sharp corner stand out and look sharper. I did a similar thing in some places with shadows instead of highlights, adding some extra darkness to firm up the edge. If you look closely at the reference image, it's there along the bilateral ridge. I could probably do more tweaking like this, but this was just a quick edit, it's not perfect, just an idea. Oh, and I changed the color ramp. Your greys were all over the place in hue, so I made a ramp where it shifts from yellow to purple gradually.
You did a really good job with this, it's quite shiny! Most of what I changed are things I picked up from experience, not observation, and you really nailed the execution of everything based on observation. I'd say this is a success.