My sizes are wrong, 6 inches is not 6 inches apparently lol
The quick fix is to change the GRBL settings for steps/mm for each axis.
X = $100
Y = $101
Z = $102
These GRBL parameters define the number of steps the stepper motor need to make in order to cover 1mm.
Another option, if the scaling is in half/double etc is to change the micro step level (divide steps into halfs/quarter steps)
If you jog 5" what is the actual measured travel?
In this thread I did an example