Ok, you did show me how the picture was going to be 'blocked' for the cover. I have seen it done this way, and also continuing around the spine to the back.
As mentioned by others, I think the scale's off on the uni-pony (baby unicorn? not sure what you'd call it..;) I'd rotate the unicorn forward, to address the leg issue. The bottom of the robe/dress seems to hang out in empty space, but you could probably reposition it. The 2nd (magical) picture, imho, doesn't work. The object of the picture is to attract the eye, and the colors tend to wash out. From observation, I've seen people attracted to a) detail, and b) bright (but not too bright) colors. Once the eye has been attracted to the book, the next thing you want to have in mind is directing their gaze to the title, author, etc. Keeping the main characters in the center works well, because you may want reviewer's comments (i.e., Riviting!, couldn't put it down!, etc..;) some place where they don't detract from the action.
Atlernately, you could scale the Unicorn, and have it lifting one hoof towards the magical character (fae, wizard, I dunno), a la` Michaelangelo. Sometimes a little twist like that might get more attention.
Lookin' good so far, keep it up.

I wish I'd said that.. The Staircase Wit

anahl nathrak uth vas betude doth yel dyenvey..;)