I didn't know Leonardo wrote anything on the subject, I have had no art history to speak of (school classes are a joke) and really haven't thought about reading up on some of this stuff before. I really should, as that's very true. I draw my figures arachnodactylic because my fingers are longer than the norm.
I tend to draw women and men with the traits I see as attractive as well, usually slender males, females with just the right amount of fat, large eyes, noses with a ball on the tip, thin eyebrows, flat chested women, soft slightly wavy hair of a light hue et cetera.
I don't think you should pass off an inconsistency in your work as insignificant merely because it's for fun, It's always nice to master something else.
I understand the drawing is small but there's always the 1 px photoshop brush. I think you added unnecessary darkness to the nostrils when you should have instead signified the wings of the nose forming the outline of the black leaving the bottom of the nostril flowing into the upper lip, the angle is too high to see that far into the nose. But if it is just for fun and you keep a lookout for it in the future it doesn't really matter. You could say it's merely style.