I also planned to perform a song I haven't finished writing yet. However, time did not permit me to achieve this ridiculous feat and I think I'm glad of that. There's not a great point in putting a song out there until it's ready, though I think that my idea was to somehow shock myself into working out how to finish it by finding myself in the middle of playing it in front of an audience.
I did manage to knock out a quick improvised blues to silence a heckler, which was fun, and which proves I can write lyrics on the moment. However, there's a difference between improvising an obviously improvised song and guessing one's way through something which looks prepared. So... I'll have to finish writing the song at home.