Thanks quisling! I finally managed to fit the shape in the grid after flipping and rotating it. For some reason I was fixated on a different edge being on the top border!
Like riversk my diagonal in cell 1 isn’t precisely corner to corner, but it’s very close and since everything else fits neatly, I think I probably have the right solution.
If anyone has a cell 1 diagonal precisely corner to corner though, let me know and I’ll go back to the drawing board!