Attached is your model created using only Sheet Metal features. But even in that case it still can't be flattened since it's not a 'broken' part but rather a 'formed' part, which would need to be done using a set of forming or 'stamping' dies.
I created a second model, next to the first one, again using only Sheet Metal Features, but this one can be 'broken' meaning that you can create a Flat Solid.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA Siemens PLM: UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.