Photos are arranged in the book in absolute chronlogical order. Evidently your files are not in chronological order because scanned images take on the scan date whereas photos from a digital camea have the date the photo was taken.
To get your photos into a book in a specific order here's what you need to do before creating the book:
1 - assemble the photos in an album and arrange in the order you need.
2 - select all the photos and use the Photos ➙ Batch Change ➙ Date to Date menu option to give them all the same date with a 1 minute separation between photos.

Do not modify the original files!
3 - select the photos and create your book. The order of the photos in the book will be the same as was in the album.