OK, now I can see what you are trying to do. In short there is no way that I know of to do what you want the WAY that you want, as in folding the existing mesh the way you describe. I would suggest that you delete the faces in red and then add a Solidity modifier to what remains. This will turn the mesh from something with just an "outside" to a mesh with both an "inside" and "outside" and then delete any unwanted faces . Another option is to again delete the faces in red and create your hem by extruding edges. Either way will mean uv mapping parts of the mesh again.

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