I really need to stop showing the corrected image at all until the 3rd sample or so is taken. Ignore the corrected image - it’s to show you how things are progressing, that’s all.
The system takes measurements from 9 locations in the camera view, and uses the combination of these measurements to compute the final calibration. What you’re looking at here is the result of taking one capture in the middle of the bed and using that alone - it’s not expected to look right because it doesn’t have enough information to do a proper correction yet.