could it be the fabric causing it? one time i had a double line with my laser---when i put a different color fabric on top of my quilt the double disappeared, removed the new piece- double again- it was a black quilt and i really had to fiddle with it= had to rig up a spool holder for it that was higher up === when the laser was too close i had double- when further away- not so much.
it took me quite some time to find a remedy-and now= if it's a black quilt i just don't bother trying to use it...too aggrivating.
good luck- let us know if you find a solution...