Hi,
Hope I'm getting this right

, open ThumbsGrid.as file and find the method named "arrangeThumbs". Here, inside this method you'll find something like:
Code:
if (cmc._x+cmc.width>w-2*hMargin)
. This is realted to the Stage.width (it is not very sugestive). Now we should restrict it to the width of 3 thumbnails. So, replace that line with:
Code:
if (cmc._x+cmc.width>3*(cmc.width+ths)-ths-2*hMargin)
Where the "3" value represent the maximum number of thumbnails in a row (actually the number of columns).
Try this, please, and let me know if it works.