After reading your post it sounds like you want to shift the guidance line vs change the implement offset so you can strip till 3 ft to left of the original row.  I assume you are using an InSight as the interface?  If you want to shift your guidance line 3 ft to the left of the original line use the "Guidance Options" button on the run screen and there is a shift option.  You can enter in the 3ft and shift the guidance pattern to the left and be ready to go without altering the implement offsets.

The implement offset you entered shifted the strip till bar 3 ft to the left which changes how the on screen map appears and where the centerline of the strip till bar is in the InSight but physically the strip till bar did not change position behind the tractor unless you made modifications to the bar from previous uses.  Hope this helps.