Notes not showing within the main app window

Just did the most recent update, and while all of my notes in the Notes app are here, when I'm in the app (on my Macbook Pro), I can see the sidebar, then next to that the list of notes. Previously there was another column that had the notes within the app. Now, the only way to view the notes is to click on it, opening them up in their own window. I'm sure it's an easy fix (at least I hope so!), but I've tried going through every sitting and no luck. Thanks in advance for any advice.