The Columns field determines the maximum amount of cards allowed per row.
Most blocks that support columns can be set anywhere from two cards per row to five. You’ll find the columns control in the block sidebar, and you’ll need the parent block selected in order to access this setting.
No matter how many items per row you have your Grid block capped at, it will seamlessly break cards to the next row depending on viewport size until it reaches the maximum allowed.
On mobile, the cards will automatically adjust and re-layout to show fewer cards per row, so you won’t have to worry about your content being too small.