If it's going into the barrel too far, you could use shims or roll peen the shoulder. If it's not on far enough, you would need to machime the back of the cylinder, or lathe back the barrel shoulder, or buy an in-spec gas cylinder, ideally a usgi one, to see if it aligns.
If it's seating too far into the barrel, you could, for now, play around with your gas locks to find an orientation that moves the cylinder out enough that the gas port is not being partially blocked and then function test the rifle.