Round the horn and lighten the color. You could also change the wavy thing you have going on with it. Also, so much sharp sketch lines on her face argh I cut myself on them :(.
these changes won't fix what is bothering me about it
what bothers me is Spike looks fine, and doing the same thing for Twilight doesn't
i did this last week too. pinkie ended up looking terrible (so i made her flat looking lol), but the side-object (a heart-shaped rock) looked fine. literally the same situation two weeks in a row. i don't understand why and i'm trying to figure it out.
the sharper horn is a personal preference with design. i can't argue about the color piece as i haven't tried it but would rather say i know it wouldn't work. i don't understand the wavy thing. i actually did re-sketch it in a larger brush size, and although it looks better sketch-wise, again it doesn't change anything.
and then the whole "trixie becomes luna's student" thing.
at this point, i'm fairly confident Twilight will become a part-time student of Luna's before the season ends