Ahh, I thought I'd fixed being able to clip out of the world! Sorry about that! Definitely something I will look into for when the judging ends.
If you want a workaround that will allow you to keep going and get to the boss, you can edit the save file with a text editor at C:\Users\<user>\AppData\Roaming\Godot\app_userdata\KTCJam2026-Aqua. Change the value of checkpoint to 0 and the value of checkpoint_area to 1. That should put you back in the lobby when you hit continue.