The double lines are caused by the tracing algorithm used just so you know.
Those types of files usually have other issues as well. Not sure what kind of software you have but what you could try doing is offsetting either the inside lines or the outside lines by half the distance between them and then erasing the original ones.
I would recommend that you decide first to go inside or outside and then erase the ones you are not using first. Good luck!
"If you see a good fight, get in it." Dr. Vernon Jones