This is because the image is not filling the div. The best way to achieve this is to remove the div block, and put the image right inside the grid. Set the image width and height to 100% and then select ‘fit=cover’.
I think that will work, but if not, post a share link and I’ll have a go at fixing it.
The image is not covering the div because you didn’t tell the image to use cover object fit. This is something you apply directly to images not their parents.