Have you ever calibrated your X-Carve and adjusted the steps/mm? If not, it’s likely that your machine isn’t completely accurate. If you use the default settings it’s close enough for a lot of work, but if you want precision you need to tweak the settings to your specific machine.
Other possible causes could be low pot settings, tight/loose belts, and so on. Since you mentioned the belts and V-wheels, the fact that your numbers are really durn close in X and Y tells me it’s probably just that you need to fine tune the settings. There’s a good video on how to calibrate the machine in this forum: Steps/mm Calibration