Good for being a first game, try to add some information about the current state of freezing because there is nothing to tell how frozen you are and how much time you gain from picking fire.
A summer mode, avoiding the fire could be nice too :)
Viewing post in Chill, Brodot! jam comments
Now that you mention it, I think there are no direct examples of how to do it for 3D,
For simple systems you can do the same as on http://docs.godotengine.org/en/3.0/getting_started/step_by_step/ui_game_user_int... you will work on a 2D viewport but controls will be shown over the 3D one when running if is inside the same scene.