This may be obvious but 'dish corrections are made to center the rim in the bike' or centered between the 'face of the locknut on the axle'. If you are saying that the rim is offset from center toward the DS then either the NDS spokes need to be tightened to pull the rim toward the NDS, or the DS spokes need to be loosened to allow rim to move toward the NDS. Which one depends on actual tension readings.

When you say "It's really dished to the cassette side", how much do you mean. 1mm is considered acceptable as rim offset from the locknut face. More than that and it should be reduced by appropriate tightening or loosening to move the rim closer to the center.

The DS spokes should end up having approx 70% higher tension than the NDS due to the steeper angle of spokes on that side. If your wheel has lower tension on the DS than on the NDS it's not tensioned correctly.