If you have your PDF in a 2 page spread format, where two physical pages are on one page of your PDF, you will need to have this corrected before you can submit it for print.
If you have based your page count on a PDF of 2 page spreads, your page count will just about double when you correct this. This will put your book into a higher page tier and could increase the cost of your order. Contact your Bookbaby Publishing specialist to correct this.
If you created your document in Adobe InDesign, here is a video that walks you through the export setting to change from spreads to pages.
If you are not sure how you should set up your pagination, here is a video that will help you understand what will lie on the left and right pages of your book.