If you click on the top icon in the left-side toolbar, the layout presets will open in a flyout menu. If you select “Standard” it should get you back to square one.
Once you get things set up the way you like you should run Window>Layout>Save as Startup Layout. Of course you can save as many layouts as you like.
One thing that you *can’t* fix, AFAIK, at least on Windows, is Cinema starting up a dual-monitor layout on one monitor … so I always have to maximize Cinema after opening. Not a big deal but annoying.