You may need to calibrate for many times at this step.
The recommended distance between the nozzle and the hotbed is 0.5-1mm.
5.3 Fine Tuning
After the initial adjustment, home the printer. Disable the stepper motors( ), manually move
the extruder to the four corners of the hot bed and fine-tuning the wing nut at each corner to level
the distances between the extrusion head and four corners. During adjustment, you can put a
piece of A4 paper(half fold it) between the nozzle and hotbed. If you can feel a bit friction when
you pull the paper back and forth, the distance is proper.