If you’re seeing that circular features in your prints are not symmetrically circular, it means that your belts are not tight enough or that they’re unevenly tight.
There is a common misconception that belts should sound like guitar strings. This is not true. If you flick the belt, you should notice it slightly vibrate back into place.
If a belt is not tight, you will need to open up the printer by unscrewing the three screws that hold the aluminum print bed, lifting up the bed and then lifting up the three surrounding panels on the printer. Make sure to remove the circuit board from the standoffs and the extruder from the bottom plate. This will allow you to lift the cylindrical panel so you can get to the motor’s screws.
Once you have access to the motors that move the carriages up and down, un-tighten the four screws that hold the motor to the bottom bracket using a T10 screwdriver. Do not remove the screws completely, just a turn or two should do. Then push down the motor while re-tightening the screws. Check to see if the belt is now tighter than it was before. If the belt is too tight, the motor won’t be able to turn properly.
After you have re-tightened the belt(s), you will need to redo the auto-level procedure as your belts’ mm/step have slightly changed due to being re-tightened. Do not edit the config’s mm/step, simply re-run the auto level gcode script.
