Here is a GIF going over the simple steps of setting an A-B Line using a John Deere 2630 Display.
Are you getting wide and narrow rows when using your GPS?
Your receiver could have a bad TCM calibration. Don't worry. It is easy to check your calibration to see if it is correct, and it is easy to re-calibrate if you are not lining up properly.
How to check your current calibration