error/difference between x and y axis in delta 3d printer

Hello friends

I have a problem on my delta 3d printer

Between x and y axis when im printing for example a cube 10 mm or 20 mm

One corner can be 19.8 mm and the other corner can be

19.3 mm...

So every shap i print is not symmetrical.

In about 50 micron difference

I try to play with the diagonal radius but it change both x and y dimensions and not only one of them.

So what can i do to solve this problem ?

Thank you all...