Comet, Nice attempt but, before you concern yourself with modeling (shading), you need more practice seeing correct proportions. I noticed a few things in your drawing that detract from a true likeness, if that was your intention. Her left eye sets back a little too far in your drawing and eye, eyebrow and jaw are slightly stretched horizontally from the model's. If you extend a line from the model's jaw, it lines up with the front of her ear canal. Also, the model's straps aren't spread apart as far as you show and your sternocleidomastoid muscle should be directed to the pit of her neck instead of straight down. Try drawing this head by eye, then lay your drawing over the reference and hold them together up to a bright window to see how closely you've duplicated the proportions. Comparing your drawing to the reference in a mirror also helps to exaggerate any differences in your drawing.

Hey Comet, I will say that you captured the likeness pretty well in your drawing. The issues you are having is, yes, all your values are too dark, but, I think the value range is pretty good. The contrast in values in the reference isn't all that much either. The reason you are having problem with areas looking flat is because the reference is flat lighting. Anytime the light comes from the front, it flattens out the details, that's why they shoot glamour photos that way because it looks flattering to women. As far as the ear, make sure you use both soft and hard edges, it's what gives it form. I did a quick sketch to show you what I mean, I hope it helps :)