Started on the rust today. I shouldn't have. Now I can't sleep at night

I had a spot just behind the pass side back wheel, going into the wheel house. I started removing the paint around it and there was only more and more and more... there's a half meter metal removed already and I don't think that's enough. It also stretches way back to the bumper, so I need to know one thing:

I haven't got my Stillen kit yet so could someone pls tell me how it's suppose to be put on? I mean, would you cut away some metal or does it fit on top of it? Haven't seen any pics of the job itself, only when it's finished and that doesn't give away much of how it's put on.

 

it just fits over top the current bumper, im almost positive.

 

oh ok... that means I gotta fix the damn rotten piece anyways