Did that with a Z-24 years ago (almost). Couldn't figure out why the car wasn't lifting off the ground until I stopped, opened the passenger door and saw that the passenger-side floorboard had been raised considerably!
I lowered the jack and stomped the floorboard down until it was normal...I was pleasantly surprised how easy it was to deform that area...not much metal to it.
Fiberglass is kind of a pain to use if you never have tried it. Have a welder patch a piece of metal onto the damaged area and coat it with roofing sealer to prevent rust...