It dawned on me that, since I am doing pencil sketches, I should use sketch paper instead of watercolor paper. In defense of my watercolor paper choice however, I had been planning to tint my sketches; watercolor paper is good for that.
Of the face parts, mouths and noses are the most difficult for me to render under normal, undistorted conditions. If I were to re-do this sketch, I would shorten the distance between the bridge and end of the nose, and reassess the proportions of the mouth. (The slant of the mouth is right on.)