Why you look like a girl or a boy

Again from Science Daily, a study saying that the the difference between a face looking male and looking female is the amount of contrast, particularly between the eyes and lips, and surrounding skin.

Regardless of race, female skin is known to be lighter than male skin. But Russell found that female eyes and lips are not lighter than those of males, which creates higher contrast of eyes and lips on women's faces. By experimenting with an androgynous face, Russell learned that faces can be manipulated to appear female by increasing facial contrast or to appear male by decreasing facial contrast.

So if you want to erase any doubt that you're a girl, use makeup to lighten your skin and darken your eyes and lips. It worked for Michael Jackson.