Floor Pan Install Question

As said above when you get to the final cut(Cudak used sand bags)and I used selftapping screws to pull the pan down to the frame.
I saw a guy that wrecked a set of pans because he cut them with the new pans laying on top of the old pans and when it got fully pulled down ended up with over an inch gap in places.
I also did my Dart with the engine and trans in place(just sealed it up yesterday)
Doug