Have you done the calibration first?
https://youtu.be/WcCNC8wExUc&t=446
https://docs.sparkfun.com/SparkFun_Opti … alibration (also do the offset and position one that follows)
The video has a few notes about darkness/reflectivity and notes that the mounting distance works best very close (10-27mm from the surface)
Is the surface being used for calibration fully flat? Any nearby sources of EMF?