It should be fairly easy to tell if your horse's shoes fit correctly. A horse with a correctly fit shoe will have a shoe shaped to the shape of their hoof. They should not appear to be standing on a platform, with edges of the shoe sticking out. Your farrier should shape the shoe to the horses hoof, then to fit it correctly to the hoof will even the edge even more after nailing it to the horse's hoof. The back of the shoe may stick out slightly from the heel, this is an acceptable practice for farriers and can help correct movement or help prevent shoes from being pulled. Finally, if you want to tell for sure if your horse's shoes fit correctly call your vet for a visit or another farrier for a second opinion.