1 Mysterious Gem (dropped from pheno encounters) plus 1 type boosting item results in 5 of those type gems
20 type gems are needed to change the HP of a mon, so you need 4 mysterious gems + 4 type boosting items to change the hidden power :)
Are you sure you had the right email address? I don't think this happens often, the PokeMMO confirmation email bot is usually very fast.
Anyways, you can have as many accounts as you want on a single email address, just try to make another one from the same email