USB transferred book does not show up

Hi everyone, hoping someone can help me...I am attempting to read a fairly large book and having trouble getting it to show up on my Kindle.

I always email books to my Kindle (11th gen paperwhite) and I never have an issue. This book was too large to email apparently, so I thought ok, no problem use the USB. I double checked that it was an .epub file, which is it. I moved the book file to my kindle, ejected the Kindle, and the book did not show up in the Kindle. Searching did not bring it up. Plug it back in, try again. It says the file is present. So I opened the kindle on my computer, & easily saw the book file (with publisher's cover). It was outside of the 'books' folder, so I moved it in in case it made a difference, but it didnt. Still cant find the book on the kindle.

Its a book club read, so im feeling a bit of pressure to keep up. Any suggestions would be appreciated! Including a better format for email maybe?