Agreed with above. Recently I heard a tv trainer say that you cannot punish a horse, like you can punish a dog and get the result you want. You CAN, however, keep asking until you wear your horse down, then give an immediate reward, like walk one time around the arena and dismount. I know this bc I own 2 gaited (KMH's) horses who never want to walk down a trail or anywhere else. It's just in their nature to amble fast everywhere.
I kept asking my 6yo gelding to walk instead, and he finally understood that I want miles at a walk at my descretion. I have also, in the past, jumped, trained English and dabbled in Dressage, so it isn't a trail rider thing I've talking about. Even bossy horses want to follow a leader.
Just keep doing it, and you will get the result you want, but it will be on your horse's timetable, and not yours.