The "zoom selection" does only support one row. This has two reasons: First, it's not so simple to arrange the other images around, if there are multiple rows. Second, this question is used very rarely, and therefore got less attention than other questions.
If you just need the selection of images, but not necessarily a zoom, please try the default "selection" and change its display/layout settings so that it displays "cards". These can be arranged in a grid, and with little CSS you can also remoce the whitespace around images. If you like.