Is there any way to change back to you human form when you use the amulet? I have tried to do this while shape changed but the only way I can do it is by resting. Maybe I'm missing something but I would really liek to see what is on the other side of the lava stream but when I attemp to rest A fire elemental pops up on the opposite bank and I can't change back.

On the right-click radial menu there is a button to stop the polymorph.