MBot Cube (DH kit): Geometric X, Y error

MBot 3D Printers
#1

When I printed a box 20x10x5mm real dimensions X and Y became 21.3mm and 11mm. Why?
When I preparing the x3g-file for the SD-card in ReplicatorG, printer MBot Cube is missing in the list (see picture). I select MBot Grid. Maybe that’s why the sizes were different? Why MBot Cube is missing in the list of Generate GCode dialog?

#2

I counted the number of teeth on the timing pulley - 18 and understand: it is necessary to use the version MBot3D ReplicatorG (18) instead of MBot3D ReplicatorG.