This specific issue is due to a previous pan and zoom setting you may have applied on a prior scene as seen below. Please note that for scene consistency, Doodly applies the "end frame" effect to all succeeding scenes. That's why you only see a fraction of the canvas.

To fix this, you will have to insert a new pan and zoom effect that adjusts the framing to how you want the other scenes to appear. In this case, the start and end frames are stretched out to fullscreen as seen below. This reverts the scene framing to the default full canvas view.