To create “columns”, you need to inline blocks and set a width on them.
For that, you need to edit your blocks, and set under Appearance panel, Position > Display > Inline-block.
And, you need to set Sizing > Width > 33%.

.wpgb-grid-2 .wpgb-card:nth-child(2n) .wpgb-card-body {

    background-color: #80808029;

    border-top: 2px solid;

    border-bottom: 2px solid;

}