I noticed with Gutenberg and Gantry there is some code somewhere that is not allowing the video to be full width. When I change templates it works fine but you can see in this screenshot it makes the embed a smaller video.
Please would you post your URL, admin id and pswd in the secure tab of your post and I'll have a look for you.
Also, Please post your FTP logon, password and FTP URL in the secure area of your post.
Please search forums before posting. Please make sure your post includes the version of the CMS you are using and a link to the problem. Annotations on screenshots can also be helpful to explain problems/goals. Please use the "secure" tab for confidential information.