Two things are obvious....
1. Someone in the past had an 1 1/2” hole saw and weren’t afraid to use it, though why escapes me.
2. I’m pretty sure there’s supposed to be a plate around where the tank filler neck disappears through the floor, isn’t there?

Blanking grommets on order as a temporary fix, but anyone able to share a picture of what the filler neck plate should look like, if indeed there is one? I’m clearly not using the right terminology on Google searches.
Ta.