When you are shading traditionally, you must squint. Squint and block out your vision partially to see those shadows pop up. If you are unable to do so take your reference image and go to a website called Imageonline.io turn your image black and white, and posterize it to level 3 or 2. This way you will see the bare minimum values which will help you block out your values. Secondly, it is much easier to go from light to dark than dark to light so pushing your values just a bit more is muuuch better than trying to go the other way, don't be afraid to push the darker areas because they're not your focus the areas in the light is. As for your proportions I adjusted the eyes and jaw a bit remember this: Nose is the center of the face, if you got the nose right the corners of the lips will be correct the corners of the nose lines up with the corner of the eyes where the tear ducts are, and the nose gives you the opposite side of the eye and the lips gives you the end of the eyebrow. The bottom of your ears lines up with the bottom of the nose and the top of it lines up with your ends of your eyebrows. your eyes are always one eye width apart (sometimes wider depending on race or face shape) also, your head is more rotated compared to your reference which might account for why everything is thrown off a bit. Apart from micro-expressions its a great sketch and I'd say with some adjustment it will be just fine.
