Indesign book, no spread where a chapter ends and a new one begins

I have 18 chapters, where I have a single page at the start and end of a chapter, when I'm trying to save as pdf, where the chapters meet, I'm getting 2 single pages and the rest of the pages are fine, they're showing as facing pages. 

How do I get it to where the last page (left page) of a chapter is on the left and the new chapter is on the right of the spread?

At present I have 2 single pages