Hello All
I recently purchased an Ender 3 max.
While trying to level I noticed that the middle of the bed plate is a bit higher then the edges.
What can I do to level that out?
Call the company you purchased it from and request a replacement bed.
They’ll probably ask how much the bed is warped and they may have return criteria (ie it’s not warped too badly that it can’t be used).
How much higher, a few thou is not unheard of. Unless the bed is ground flat “AKA a very expensive printer” it is unlikely to be totally flat.
Yeah its not much higher, we are talking much at all.
Another point to remember is that when heated the centre is directly over the heating pad and tends to expand a bit more then the rest so it will be a bit higher then the rest.
I do think that is what is happening.
Question is how do I make it better, more flat.
The sheared plate that these beds are made of are not super flat, that is why expensive machines $$$$ have ground beds. Unless it is more then a few thou higher, like more then 0.004" I wouldn’t worry about it, it really doesn’t make a lot of different. Mine is off a couple of thou and is no problem. Some people will measure the difference and shim the surface corners with something like paper to level it out. If you clamp a flexible plate onto a warped bed the warp will carry through. That is one of the advantages of using a glass bed, it is generally flatter and resist bending somewhat.
I confirmed that the bed is actually flat, it looks great actually.
The glass bed is a bit bowed in the middle. So I used some tape on the sides and it helped enough that its not a problem, still not as good as I want it but it works.
I’m looking at using some glass and PEI, I did that with my last printer and it worked pretty good. I was hoping that I wouldn’t have to do it with the creality but maybe I do 
How much is your bed off by?
As @Loosenut indicated, you can be off by a few thousandths of an inch (0.2mm seems to be Prusa’s guideline for what is acceptable) and still be okay to print.
I usually print with a raft and this really evens things out and gives me a flat first layer.