If the dimensions are not to your liking, there are a few quick tweaks you can implement to improve your results:

Novice: Simply scale your object before printing. If your calibration object measures 10.5mm, and it should be 10.0mm, scale the object down to 95.24%. (10.0mm x 100%)/10.5mm = 95.24%.

Intermediate: Edit the firmware to reflect a more accurate steps/mm calculating the required steps/mm vs the actual steps/mm.

Expert: Change both the feedrate and flowrate as they dictate how much plastic is distributed per mm. These settings can be used to fine tune your printer once you are close in calibration.