500mm bed mesh with full width hump. Gantry issue?

This is the bed mesh using a super pinda on my 500mm bed. I watched the video and if I am understanding it correctly, the four corners are pretty close to the same plane. I think this means the frame is pretty square. However, there is a pronounced bow from front to back.
Not sure what the best way to attack this is. Maybe loosening the screws on the Y access rails and moving the gantry back step by step tightening the screws as I go? I also heard him say that you should not install all the screws in the rails. Should I be removing some screws?