I am using the iOS YouTube Player helper (https://developers.google.com/youtube/v3/guides/ios_youtube_helper) and it works just fine but the preview image is not the size of
This solved it for me:
In the Assets folder there should be an html file named "YTPlayerView-iframe-player.html"
Replace the existing code between "style" tags as shown below and this will make sure the Player fills 100% of the YTPlayerView:
Hope this helps a bit! Have a great weekend!