The feedback grid testimonial widget is responsive, which means the layout changes based on the width of the container it's in.
The grid will display different layouts for the following widths:
Over 1140px - 3 columns
Between 760px and 1140px - 2 columns
Under 760px - 1 column
If the grid isn't displaying as many columns as you wish, you may need to increase the width of the container size that it's in.