Make sure your calibration cap is clean. A dirty calibration cap can affect the results of the measurements, as your Colourpin will be calibrated incorrectly. In this case, clean the lid.
If you have access to official NCS samples, try to measure 20 of these samples and see what the results are. If more than 1-2 samples show the wrong results after measuring, follow the reclaim process here (you need to scroll down to "Return policy for Colourpin II/SE" and then press on the Complaint form".