I've never used AmTak finish, so I'm not farmiliar with the cure time. If your workspace is less than 70*, it will take longer than normal to cure.
Did you pour all the solvent off the Testors before you mixed it in? That could be the reason for the slow cure. Possibly, you used too much pigment, also adding to the cure time. For epoxy, application thickness has no effect on cure.
As for the fingerpring, we've all done it at one time or another! Next time, stick your thumb on the leftover stuff to see if it's cured, not the rod.