My tooth gard melted & its useless now!!! :O?!

I bought an expensive tooth gard to stop myself grinding my teeth at night.
When i went home i used it and later the next day i decided to sterilize it to make sure that
no germs were on it that would cause decay.
So i scalded it with hot water & then it kind of melted and became all bent out of shape.
The edges became all warped and super hard. Its useless.
The dentist hadn't warned me about this or what was the best way to clean it.
He gave me just half of my money back...but i feel cheated.
What can i do?
Its was so expensive & i'm an unemployed graduate.
GRRRRRRrrrrrrrrrrrrrh...!
Its not fair.