contact sheet not letting me format how I want

Hi, as seen in the photo below i am trying to create a mosaic (image 1) through using the contact sheet, but i am wanting the images of the colours pink and purple to alernate (image 2) in my folder they do alternate but when i put itnto the contact sheet it reverts it back (back to image 1). i would be greatful if someone could please help me out. kind regards Elise