Anyone handy with vector/SVG/DXF graphics/CAD stuff...?!

...because I ain't!
Pretty please could someone help point me in the direction of solving my problem 🙂

I've uploaded a selection of pics related to this predicament here rather than fill the forum with boring photos:-
laser cutting related photos
There is an example of the kind of thing I have made recently using his laser cutter - the shapes I supplied were drawn on paper and scanned in - which he is no longer able to/wants to do.

Background:-
I am a welder/metal basher/sculptor type who isn't completely hopeless at tech stuff, but struggling with vector/svg/dxf stuff which is all new to me!

My aim:-
Be able to send freehand drawn (on my graphics screen thingy) organic shapes as DXF files to my mate with a laser cutter who can then load into autocad, send to his laser cutter software and cut the shape in sheet steel for me...simple, or so i thought.

My kit:-
-Old Macbook Pro which works well enough for this setup
-Huion graphics screen thingy bought for this purpose
-I do have a Pixelbook Go that I could hook up via HDMI for chrome based programs.

Software:-
Don't really have any spare dosh to splash on software and have been using Inkscape as it will save to DXF etc

Problem:-
Everything I send my mate comes through as double lined - I.e. one single line i draw on inkscape is coming up with an inner and outer line.
I cannot work out in settings how to rectify this, have sent different file types to him etc...

Can anyone help or recommend a simple solution to my problem, whether it be a piece of software I've missed or knows how to use inkscape properly?!

I can just about find my way around sketchup and have done a bit of CAD in the past.

Here is an example of the kind of thing I have made recently using his laser cutter - the shapes I supplied were drawn on paper and scanned in - which he is no longer able to/wants to do.
Rusty Cardoon gate