For best results, use landscape orientation.
Mirror, Mirrorīy default, turning on AirPlay Mirroring displays on your TV exactly what’s on your iOS device’s screen-which also means it’ll be in portrait orientation (with black bars on the sides) if your iOS device is. When you’re finished, click the Stop button. Whatever you do on your iOS device is both mirrored and recorded in QuickTime Player.
Install the software per the developer’s instructions and make sure it’s running. Examples are Reflector (my favorite), AirServer, and X-Mirage.