i wouldn't like to use overscan to correct problems involving "3 inches" of border - that suggests a different problem. stretching it via overscan settings will probably produce scaling artefacts.
@sonicmartin76 what videomode are you using in config.txt that produces the borders? a 1080p mode should be handled correctly by your TV without significant borders.
ps i would suggest setting the resolution via raspi-config/the config.txt as per https://retropie.org.uk/docs/Pi4/#issues-using-a-4k-tv - remove any settings via runcommand if you have made them, as the fix needs to be global to the system, not just to a specific system/game.