I just received all the supplies I need to make compact mirrors on my button maker. I am very excited.....But theres one problem. There is a part called a shim which I think is used to stablize the mirror but I'm not sure how it works. I just made a mirror and put a shim between the shell and the mirror. It came out looking good but the shim isnt secure inside the mirror. You can hear it sliding around inside.....Does anyone know what I'm missing here?