Great! To get the print to the middle, the point of origin (x=0,y=0) needs to be same in Marlin and the slicer you are using. If you use same Marlin config as i do, the origin is in bottom left (home) position. Just confiure the slicing sw to have origin at 0,0.
I'm thinking about changing the origin to the center of the plate because setting z-gap is harder when the nozzle is at the corner. Not a big problem, it's fine now so haven't done anything yet...