"Third to last"

I was confused, I meant "second to last" indeed, but you are correct.

By that I did mean you should have called it the second or third sentence instead, not that antepenultimate means second from last. Doing otherwise in a four-paragraph passage (and nearly any other context, frankly) is absurd and makes most people think you’re trying to sound well-read, and you end up where it is unclear even to yourself what you said.