Zoom - you can zoom in and out of your canvas by pinching in and out on your trackpad, or by clicking the plus and minus buttons on the zoom. If you click on the zoom percentage (ex: 80%) you will see the following options:
Zoom to Fit: Zooms out on your canvas to show all of your notes/themes
Zoom to 100%: Zooms in on your canvas to show notes at 100%.
I lost my sticky notes on my canvas, how do I find them?
The first step would be to "zoom to fit" and see if your notes were moved out of your current view.
Next, you can search for a note at the top right of your canvas. This will filter the screen to find notes that use the keywords you type here!