Guidelines for Unbending a Part
Keep in mind the following points when unbending a sheet metal part:
Best practice is to use a planar surface and not an edge as a fixed geometry reference.
The part-level fixed geometry reference is used as the default feature reference.
When you toggle from automatic to manual selection, all the available bent references are added to the Bent geometry collector.
You can use the Flat Pattern Preview tool to open a window with a preview of the sheet metal model in an unbent state.