You might need to take the belts off and verify all the steppers are working. Seems like one might not be.
Are you using my firmware on a ramps board? what drivers? If you step rate is too Low it will produce jagged lines.
That actually just looks like there is something under the paper. Do you happen to have a small dry erase board and marker to try it on?
Do the axis move smoothly when the belts are off? It could be a rough spot on the conduit as well