For accurate recognition and cutting it is important that the camera is aligned as vertically as possible.
To test the alignment, move the camera over a mark on the table then raise and lower the camera. The mark should remain centered under the camera. If the mark moves away from the center of the camera then the camera should be re-aligned.
Below are examples of bad/good camera alignment.
If the camera is incorrectly mounted, the marks will move away from center when you lower/raise the camera.