I have made one shoe before. I used some fondant to make a mold to dry the sole on so I got a nice shape to it. I spent quite a while shaping the fondant mold then wrapped it tightly in plastic wrap so I didn't waste it all. it was basically a slope with a flatter bit at the top and bottom for the heel and toe.
I think this pic of the almost completed shoe shows what I mean about the shape of the sole.
Other than that I think you have done a fantastic job of both the shoe and the whole cake!