Hey, not a bad job on spotting the shading to create the form. But I would check your proportions, it looks like you've turned your head to the side to draw the side of it, rather than draw the whole thing face forward.
Also I tip is to periodically turn the picture upside down to spot mistakes in the proportions and symmetry. If you have a mirror close by (I now have a small mirror on my desk) reflect your drawing in the mirror and take a look, this can be done with all of your drawings. This is a good way to spot mistakes, and I use it everytime I can. For example I was drawing a skull last night and knew there was something wrong, but couldn't work it out, so I looked at it in the mirror and instantly saw it was too long vertically - it didn't turn out perfect but it was much better once I had seen the large mistake.
Good luck and practice make perfect, remember that!
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