I'll ride anything from 13hh to over 17hh, and I'm 5'11". I have and do ride with a really, really long leg, so the horse that would "fit" me by English standards is 16.2hh or better. My favorite horse is like... 15.1hh, maybe 15.2hh? I don't care. I ride child ponies, as funny as it looks. As for how wide your horse is, he'll gain muscle tone with frequent and consistent work and exercise, like any creature. :)
Think of it not as a failure but as a success in how not to do it.
Don't look in a horses mouth for a gift.