Hi Phil,
Go into the rendering settings screen and uncheck the box near the top "run full-screen at this resolution". That should get you back to windowed mode. If that box is not checked, then try to use your mouse to pull the corners or edges of the screen to a smaller window. If that still didn't work, the green arrow to enlarge the screen was clicked by accident. That is currently a bug in that you can only recover from that by going to the output folder -> preferences -> & delete the X-Plane Screen Res.prf file. Next time you start X-Plane that will be reset as a window.
In 2D cockpit view, you can only move the view up and down. Try 3D view (shift + 9), then use the period & comma keys to move in and out. You can make that your default view in rendering options by clicking the button for "forward view with 3d cockpit".