I made a batch of white candy melt candy clay about a week ago. I took it out today and it is fine for modeling but I need it a little stiffer for my cricut . It cuts fine but when i try to remove the cuts they are too soft and stretch.

Can I just knead in some powdered sugar to stiffen it up? Or will that mess it up?

No, you don't want to add any PS to it.

Pop the mat in the fridge or freezer for awhile with the cut outs on it. Once it set ups again, you should be able to get them off the mat without distortion.

Rae