Wow, that's a feat to draw that large for this assignment! It can get tricky to keep your proportions in check drawing at that size. Maybe scaling down a bit can give you more control. Otherwise, just really slow yourself down in the beginning. You may need to check, double check, and triple check your measurements, using multiple units. If you're moving too fast it is much easier to miss something or measure incorrectly. Just some things you could try, I think you did great with this, especially considering how large it is!

Woah, what a beautiful (and complex lol) pick! I think you're definitely on the right track capturing her flow and confidence. You already got down the curve and simplicity of the head/face shape, and noticed the defined shape of the hair's curving borders. Though the inner part of the hair can appear more chaotic and without rhythm, I think there is still a hierarchy defined by line weight that follows the flow set by the outside borders. I think using a middle weight line to define this, echoing the outside curve, can definitely help with reinforcing the flow of the original piece.

Nice work, the light and shadow looks great!

These look good, but it seems like you drew true to the photo rather than draw inspiration from them

It can help to make a few indications of proportions very lightly in the beginning. You can draw an “envelope” around the object, or make it up out of shapes. Whatever makes the most sense to you. Just keep it light!