There is no practice green unfortunately, not for the want of one mind. Hopefully WGT will finally grant the wishes of many and deliver one to us soon.
The reason you are remaining a Hack is because you are not playing ranked rounds. Practice round scores do not count and therefore your average will remain static.
Get yourself playing some ranked rounds and you will soon progress up the rankings. when you do progress the first thing you should buy is a better putter. The putter you are given isn't particularly accurate, the upgraded club should see your putting improve. It does however take a fair bit of practice.