Thank you! It's really weird that the breath didn't work, did you beat the boss and get the message telling you how to use the breath? The directions in the game aren't very clear, but you're supposed to follow the pulsating rings for objectives. You can also use the Esc menu to rebind the breath to something else, if X doesn't work for you.
Either way, I've updated the game a bit in the grace period, adding a bunch of additional audio and visuals, in case you feel like giving it another shot!