Sheet metal template?

I was cutting out the rust of the rear quarter panel (passenger side) in my 68 dodge dart (post). I outlined the bottom left corner area where I was going to cut, and I tried to stencil out some type of template before cutting it but it seemed very difficult to do due to the little curve and angle of the corner. So I figured I would cut it out as then trace out the cut out and just work with the sheet metal until it fit correctly. Only issue was after talking off the front piece of sheet metal (full of rust through holes) I noticed that the back sheet metal was also very rust, so I cut them both out. I tried to make a template but I don't seem to be getting a good fit.

I was wondering if anyone had a template for that area? Or any tips on making a template? Thanks

By the way, I got a hood from a geo for free, so I was just going to cut out sheet metal from the hood, would it work?

Thanks!!