u/Extension_Cut245

Hello. I'm no knifemaker, but could use advice from one. I'm in the process of surface polishing a japanese gyuto(sakai kikumori nihonko, around 63 HRC), and since the knife had some scratches, i started with a Atoma 140 diamond plate.

Came to find out the stamped blade has some minor concavity/convexity to it, as on one side, only the center of the blade was getting touched by the stone, and just the outside of the other side. I dont want to admit how much time I've spent trying to level the blade, but would like to know what i could use to speed this process up in the future? I need absolute flatness, and precision.

Or does it just have to take this long? Goal is to get a mirror finish by the way.