printed X and Y are not at the same scale

Hi everyone,
I tried to print the 20mm cube, but the result of measurement shows that the cube's X is 19.9mm, Y is 20.11mm and Z is 20.05mm.
I spent a lot of time at adjusting the rod length and radius at marlin, but it did not work.
Also, I measured the length of the 6 rods, those were at the same length.
Whats wrong of my printer? It has trouble my for a long time.
Thanks

I'm not sure what rod length has to do with print size accuracy?
It is controlled by the firmware. in your steps per mm.
What model device and firmware are you using?

That being said, I doubt you are going to get much closer then you are, hard to account for shrinkage from filament to filament, and if you do happen to get it dead on, it will change with your next roll.

I am using mini kossel with marlin
thanks