The intersection of the cylindrical neck with the bottom plane of the jaw is a curve. Your drawing shows it as a straight line or it's been left out altogether. It's helpful to imagine the curve that's produced by partially cutting a large diameter tube, representing the neck, at a slight angle with a saw. The jaw's bottom plane isn't perfectly flat but imagining it as a plane, the saw, is easier than imagining it as part of an even larger cylinder that cuts the smaller cylinder of the neck.

Where's your construction?

Very nice!

I see that you used your thirds construction to locate the swing's seats horizontally, relative to the length of the top bar. Your thirds construction is correct but can you prove it is?

Where's your horizon line?

Nice attempt but have you tried superimposing your drawing over the reference image to see how your proportions differ from it? It's a very good way to train your eye to see more accurately, if that's one of your goals.

Interesting how a slight change in head proportions completely changes the facial expression.

Fine example of a slick, photographic impression but I prefer an image that expresses more of the individual who drew it.

Try building this pose using modified blocks to shift your focus from its contours to its solid forms.