Mbot cube dual XY axis calibration problem

Hello,

I have a problem with my printer, the printed pieces are slightly smaller than they should, like 5% but only in the X and Y axis.

Is anyone else having this problem? I have searched in the net for the procedure to calibrate the steps / mm, but it seems that this is not possible for this kind of printers, has anyone found a solution for this?

Best regards.

Juan