you should focus on the structure of the face, rather than just the features. Heres a rough edit. It still has likeness issues cause I didnt really measure it.
try tracing over your reference just to get an understanding of the structure; where the face is broken into different planes. Thats what you should focus on. I mean like this
(notice I did it kind of bad on purpose, cant do all the work for you, you know).
I also have to second facets advice about putting down the 1px brush. Focus on shapes.
EDIT: what exactly is your process in drawing this? Do you start with the outlines? You seem to be committing your self to outlines too early. Even if you do sketch out some outlines, you dont need to commit yourself to pixel level perfection at this stage.