You may want to recheck your pots with how the instructions say to set them: X-Carve Instructions: X-Controller and verify your pot settings. While you are verifying that, also verify your micro-stepping is setup. I think it’s covered in the same section of the instructions.
You may also want to verify your steps/mm setting. If that is off, it could show as an increased feed rate. I think the nominal is 40 steps/mm so if yours is set to like 60 steps/mm, to move 2 mm your machine would command to do 120 steps where you should be doing 80 steps. Those are your $100, $101, and $102 settings for GRBL. Check out this post for calibrating your steps/mm.