(If you already know this, kindly disregard. Quicker to just say it in case you don’t than to wait on the reply process.)
When you click in YT to get the embed code, look down on the bottom-right and you’ll see there’s a ‘Customized’ option. Just type in the required width (I’d say between 400 and 440 for your set-up), and the height will set automatically. Then copy the embed code.