When the car running on y-axis works fine, we added the block in which the servos are fixed. We had some problem holding pens against the fan on the servo. We use small plastic boards drilled with holes and weave it to the servo fan using fish line. In other not to break the servo, we thinned the center of boards and use the original small screws that come with the servo.
After that, two boards are screwed together pressing and holding the pen and rotating according to the servo movement.
We changed pens with smaller diameter and adjusting angles in case of the boards crashing into one another when rotating, since we hadn’t given them adequate spacing when inserting the servos side by side on the wooden block. Sponge filled in the gap between the boards helps hold the thin pen more firmly.