Same problem here. The heated plate is not exactly flat.
Fix #1 - Do the rails so the bed is steady.
Fix #2 - take some brims from a prints and use them as a wedges until you get a good print. I created a single layer square that goes to about an inch from the edge all the way around and I print that to see where the wedges need to go.
Fix #3 - aftermarket glass plate.
(ordered and waiting for https://www.amazon.com/GO-3D-PRINT-Borosilicate-Snapmaker-Printer/dp/B08XNDYR81)
(Currently using Snapmaker A350 Creality Glass 310x310 Holding Brackets by rvanemon - Thingiverse)
I don’t know of a better “fix”. I really miss the manual leveling on my Ender 3. So much easier to adjust if it is just a bit off. And massively less time consuming.
Note - I have had several comments in the past about how the company should fix it (on other issues), and, I don’t disagree, but, that is a dog that may never hunt, so, juryrig is my go to.
Good luck.