Bed leveling is the first suspect, but I would also make sure that the x gantry doesn’t wobble, moves smoothly, and is level to the bed.
Check the y axis to make sure there’s no wobble and the bed moves smoothly. Also make sure the rest of the frame is tight and square and the belts are tight.
Leveling can be a pain to get right on the ender3, but loose screws, flat wheels, ect will make it impossible.