Although submitting is closed maybe try to contact Steam for the festival today and see if you can use the new demo to present the game. This event is one of the biggest this year and it'll be a huge lost opportunity. There is still time until it starts.
https://partner.steamgames.com/doc/marketing/steamgamefestival
You have the new upcoming demo, a steam page and etc, so you're pretty much eligible I hope to submit for the event. Miracles might happen, I hope!