I don't think the boot floor on a Seat ST is the same as a Golf (Estate).
I’m guessing there are slight differences but if it covers 95% the edges don’t matter if not perfect as it just for large flat items so not going to lose anything but will protect the metal from scratches.

I’m thinking I might just get the rubber boot liner and trim the lip off...or even just a piece of car style carpet...failing that I might take the bottle of tyre rubbish I’ll never use out and use the wheel well for my site equipment and keep the main boot free and clean