Did you export the .pck alongside the .exe?
Yep ='(
I tested it on an another PC and it worked, great app =) I had fun playing with it, and the look is awesome =)
You can embed the pck file in the exe in godot. That way you only have one exe file.
Just try to mess around the export settings. There is a checkbox to embed pck file in the executable for all platforms, including Linux. (is not needed in mac)