Experimental Snapshot

I need help immediatelly! yesterday i created a world that i thought it would be a 1.18 snapshot and i got a very good progress on it until i saw bedrock around y=4 and i was confused for a while until i discovered you had to INSTALL the snapshot to play it, since i was afraid of a world corruption i created a backup and installed it but them i can't play the world anymore, how do i play the 1.18 snapshot without losing progress