When printing a booklet, keep in mind that the total page number (including cover, back cover, table of contents, etc.) must be a multiple of 4.

Although 108 is a multiple of 4, the behavior you're describing is that of a booklet with uneven pages, which leads me to believe that perhaps there 108 pages of content, but not 108 total pages.

Can you confirm this? If this is so, just add blank pages at the end of the document until you have reached an amount which is a multiple of 4.

If my assumption is incorrect, an easy alternative would be to print the cover and content separately.