To check the piston rings properly you actually need to remove the rings carefully from the piston, slide each loose ring down the piston sleave for about 5 mm, and take measurements of the ring gaps with a fueller gage. Unfortunately I have no idea what size the ring gaps on these scooters are suppose to be.
When the ring gaps are bigger than prescribed specs, the engine will loose compression at the ring gaps.
It will also make sense to hone the piston sleave with a honer.