Issue in converting a .png file obtained by common lisp-vecto functions to AutoCAD

Question

This is a very specific ask. When I run this code:

(DEFUN TRIAL (FILE)
          (WITH-CANVAS (:WIDTH 100 :HEIGHT 100)
            (SET-RGB-FILL 1 1 1)
            (SET-RGB-STROKE 1 0 0) (SET-LINE-WIDTH 2.0)
            (ROUNDED-RECTANGLE 20 20 50 50 4 4)
            (STROKE-TO-PATHS)
            (FILL-PATH)(CLOSE-SUBPATH )
            (SAVE-PNG FILE)))

I get a png-file with a rectangle in red

But when I convert it to AutoCAD file (.dxf) I'm not able to see the lines, can anyone let me know what I am doing wrong.Also I want a single line if I do 2.0 thickness in line-width I am getting this, double lines which I dont want[

Thanks in advance