Notejoy allows you to easily customize the width of the sidebar, notes list, as well as the Chatter bar, History bar, and HubSpot bar.
Simply mouse over the edge of the pane and drag it to your desired width. Notejoy will save your width preferences for the next time you come back to Notejoy. Each pane has a minimum width to prevent it from becoming unreadable.
And remember, you can always use Focus view to hide the sidebar and notes list entirely to focus just on your current note. Hit the magnifying glass in the top-right corner of your note to enter Focus view.