This is a drawn metal part. SolidWorks can't flatten these types of parts. It has metal deformation in two directions, with stretching and compression of the metal while forming. SolidWorks sheet metal is for parts that can be made with a brake press.
You will need a program such as Blankworks or Logopress to flatten your part.
You also need a part with constant wall thickness. The one flange on the part with no radii violates that requirements. There are also issues with the perimeter of the part.
This is a large part of pretty heavy material thickness. Is the plan for this to be stamped in a progressive die? Or will it be built it up in pieces and welded together?
If welded from plate I would remodel the entire part as a multi-body or an assembly with parts. Splitting up each of the walls into their respective shapes to be welded. Use the original as your template.
You may see some similar type flattening in my website;
We still didn’t upgrade to Swx2012. So I’m unable to open your files. If you send them in Parasolid/Step… format, I could show you the flattening.