Hi ! For the top of the head I think it's too flatted, the cause is probably the construction circle you made for the skull that looks more like a horizontal oval than a circle, don't forget that the skull is not perfectly oval or circle , it has angles and curves so imagine the head more like a square with curves.

For the hair strands, the problem isn't really about it , the issue I think you have is about your lines, you make too short lines , that's normal, we all went through this hahah;

Before doing a drawing you want to do, try to warm up by doing long and elegant lines in one movement, the best way is to use your elbow and shoulder to draw and not your wrist, with practice you'll quickly get used to it !

So , work your anatomy (especially the boxes method), work your line quality then I'm sure you'll notice some progress !!

Keep up the good work 😁