My first guess was going to be that you’re selecting either “inside” or “centered/on edge” (can’t remeber exact wording, on phone) as opposed to “outside” for your outline cut, but those would produce a shape that’s off by either one or two times the bit diameter.
Have you calibrated your X and Y steps/mm ($100 amd $101 parameters) recently? Are you sure your jogs are moving exactly the right distances?
Does your machine have set screws on the stepper motor pulleys? If so, check them all for tightness (in your case, especially the X and Y).