The width of the additional image container is set as a percentage of the center column width according to how many you have specified per row, or how many you have, whichever is less.
Since they are up next to the main image, there can never be enough room to display them all as intended (the % width does not allow for the main image taking some of it).
What you need to do is explicitly override that width using !important in your stylesheet. Add a rule like
Code:
.additionalImages {
width: 20% !important;
width: 120px !important;
}
You can use either of these specification methods, adjusted as desired to fit the images. Set the number per row to what you want.