I'm surprised that they make one that doesn't fit. Looks like it needs quite a bit (like 1/8" on a side) to even come close! Enlarging the hole may help, but you may wind up with a really loose and unacceptable fit too.
In addition to the two options P32 mentioned, you could always try to source a new buttplate in the hopes the trapdoor you have fits. That probably has a lower probability of success as you have the new variable of the buttplate having to fit the stock you have to meet.
I'll look through my pile when I get home from TDY and see if I have a spare for you.