Thanks for taking a pass at the game!!
I'm excited you played long enough to collect all three keys, and yes sadly there is a known bug where the boss isn't activated upon collecting the three keys. Once you collect all three, revisit the center room (where you dropped down into at the beginning) and you'll see the keys hovering around the boss. The idea is that you can interact with the boss to begin the fight at that point, before the boss has fully powered up. Unfortunately we weren't able to submit the bugfix in time. The boss fight will start regardless once the boss reaches 100% power (which happens after about 15 minutes).