I doubt that .008mm discrepancy is causing your lack of compression.
The gap allows the rings to expand when hot w/o closing the gap completely and swelling out against the cylinder too tight. Compression should still be good when cold and best at operating temp when the ring ends touch (ever so delicately) at the gap and make a near perfect seal.
If the new rings are installed and compression still sucks, I’d look real hard at the head to cylinder seal and try your compression tester on a known good engine to see if it’s giving accurate pressure measurements. Maybe it’s messed up and your compression is fine? And the engine has a totally different reason for not starting. Weirder things have happened.