I'm thinking that you don't have the ring gaps aligned correctly with the locater pins in the ring grooves. Get some 2 stroke oil on your fingers and have plenty of oil in the ring grooves. Wipe some on the inside bottom of the cylinder. Align the ring gaps with the pins in the groove, they will be toward the intake side if the piston was installed correctly. Pinch the ring on the opposite side of the locater pins and start that edge in. Be careful with the rings, don't force them, then slide your way toward the ring gap. It's a ***** but can be done.