Slider doesn't show 9 pics in 1 box

Hi, I have chosen thumbnails for the instagram pictures. I want 9 pictures to show in one square. So 3 rows with 3 thumbnails.
Now there is one row with 5 thumbnails and the second row with 4 thumbnails. There is enough space for the 3th row to make it a square. What can I do to make it a square with 9 thumbnails?

https://www.ads-software.com/plugins/instagram-slider-widget/