That looks a good tracing!
Because of the hollows, it's awkward to see the tree width you need. Just lay your template on another piece of paper then with a ruler draw a straight line from where the top of the wither starts to curve downwards to the widest part of the shoulder, on both sides. If you also draw around your original outline, the whole lot then shows the gullet angle you need (straight lines) and the also amount of gap to be filled out with flock.
Having the gullet angles matching your straight lines means the tree points sit neither inside the horse's shoulder, to impede movement, nor outside, to allow the saddle to rock back and forth, important when there's a lot of stuffing behind the shoulder as it's usually soft enough to allow some movement (it has to be fairly soft to allow the shoulderblade to slide underneath when the horse's front leg extends).
You can see the horse's unevenness from your template (nothing to worry about - that's very common) which a decent fitter should be able to take into account when reflocking so the saddle sits level.
Hope that helps :)