The camera calibration process in Luban is very difficult to do accurately due to the excessively small size of the box that needs to be click-and-dragged into position. I found it was impossible to eliminate visible quadrilateral distortion without a lot of trial and error and repetition. It would be better to overlay the calibration control square on the main bed image which is much larger, but alternatively the calibration window could be made resizable and/or a zoom control added.
You can zoom and pan that view. Just like every other view in Luban.