repeat making your part using extrude and extrude but use the sheetmetal template.
Then use Sketched Rip feature, and unfold/flat pattern will work.
I did convert your file and it did work. The thickness has to be consistent and you must create a rip feature to make it unfold. If you start with a sheetmetal part, it will work fine.
A cup cannot be unbent because it requires material to be stretched to form it. The flat pattern ability in Creo requires that parts be be made of parts with tangent areas of uniform curvature.