If the line is too thick

1. Check the focal length with the provided focal length ruler. Correct as needed.
2. Check that the light at the laser head is emitted from the center of the nozzle. You can refer to How do I align mirror 3>>.
3. Ensure the focus lens is clean. You can refer to How should I clean the Focal Lens?>>. 

If there is a double line

1. Confirm that the laser spot at the 3rd mirror is right following Unusual laser spot>>. Correct as needed.
2. If the laser spot is right at the 3rd mirror, check whether the focal lens is clean and whether laser is emitted from the center of the nozzle. You can refer to the article "How to align mirror 3>>".