Camera calibration

That camera is only 1920 x 1080. Assuming that it gives you the full resolution when capturing, the best possible accuracy you can hope for is about 1.5 to 2.0mm - you have about 1 camera pixel for each mm of your bed size, ideally you need two or more for 1mm precision or lower.

If the image looks stretched in the middle or curved, it’s a fisheye lens.