Welcome to SolidWorks forums Ed.
How are you exporting the file: Thru part or thru drawing. Please attach the file and exported DXF file to check the issue.
Please use "advanced editor" in case you want to attach any files.
You might also find this post helpful for your future reference.
Not sure if you're saving from a drawing or saving from the part.
The best method is to save from a part that you've created a flat pattern for.
Open the part then go to file>save as
Pick dxf (or dwg which ever is best for you) and then click save.
On the feature tree you'll then get the following image...
Make sure you have all the options cleared except for "Geometry" as show in the image.
That should give you a clean flat pattern to work with.