just use the free slect tool to make the shape you deisre, its that easy man :3 and it lacks pixels too. but after you fill the color on the selected shapes, brush the sides to remove more pixels.
a unique design there, strikas. but if i were you, i could reconsider fitting the eye's quality with the head and remake the back rather than a large big circle. but overall, nice head. i would rate it as 7.5/10 and would sell it for an overral price of 4.5k unless changes are done