I personally don't understand why Amazon doesn't use the same categories in KDP as they do on their site, but you can have them update your books to the proper categories pretty easily.
- Pick the closest category available and hit publish.
- After the book goes live, copy the ASIN. Then, go to Amazon and look at similar books (especially paperbacks) and what categories they are in, and choose the 2 that you'd most like to be in.
- Then, in KDP, open a support ticket, paste in the ASIN, and then write which categories you'd like your book to be. (Include the full path since it will probably be a subcategory.)
They'll usually update your book w/i about 48 hours. Some folks have been reporting that they won't always update categories anymore, so it may depend upon who you get to answer your support ticket, but that method has always worked fine for me.
Note that there are also some categories that you can only get your book in by using specific keywords in your metadata.