Will be moved to scraps eventually.
Someone a while back asked me how much shrinky dink material actually shrinks during the baking process, so I took some before and after photos of my latest charm. A good rule of thumb is that you will end up with something about 1/3 the size that you started with. You can see here that my charm went from about 4" to about 1.5" inches during the baking process.
Please note that I use shrinky dink brand sheets (the "ruff n' ready" type), and I bake them according to the included instructions. I can't vouch for any other brands or baking techniques.
(If you don't know what a "shrinky dink" is, google it; it's a pretty nifty material)