Flatening a part....

Hi there.

I struggle massivly to get a problem solved and need some advice. (I´m no Pro, just a home user)

I designed a seal for a part that will be printed in TPU, for this it must be flatend.

I builded it that way to get the correct measurements done and now i wan´t to make it flat. But everything

i tried failed :( when i tried it with the Bending Tool it wont get completly flat. Unwind stays gray and i cant use it,

so i tried to reverse build the part to wrap it around a dummy....but this always merges the parts.

Even tried Sheet metal function but had no luck.  Maybe i´m to dump ^^

Any suggestions?  Thx in advance