so i FINALLY figured it out.
When i tried 691.2 torr, the final answer i got was 218 L, which is still not correct.
then i tried something new: i multiplied 23.8 torr by 2 because the problem said there was excess water, so i guessed that there would be 2 H2O molecules for every 1 C2H2.
well, 715 torr - (23.8 torr *2) = 667.4 torr, which is 0.878 atm.
and then i got the answer 2.26 L.