ok, go to File -> Options / Preferences (or whatever it is called)
change to the tab 'printing' and set overfilling to 0.500mm
the values for paper calibration are -0.400mm horizontal and 0 vertical
took me a while to find these settings. now all of my discs turn out perfectly labeled (centered, no white ring on the outer side)
However, make sure the images (labels) you use are good! they should already be centered and should not have any white boarders.