Layouts are infinitely long, they expand to show all content in the collection.
The layout can have two columns -- and a cell shape (aspect ratio), but a layout does not have a row count and the content shown in a layout floats above the background (no lock).
Margins and top nav can take space too, and will interfere with "entire screen" --
And card design can play a part. If you're using full image for the card, it should be good -- but a card format with image top, left, or right also has an image aspect ratio on the card. So there's an interplay there as well.
Any images you'd like to share?