Help with epub file size

I have a compile question. I didn’t have any trouble converting my two longer books into an epub file with a file size of less than 10MB but for some reason I can’t seem to convert my shorter book into a small enough epub file.
Are there are any hints on shrinking this file size? I’m so confused and really could use some help. Thank you!

It’s quite difficult to exceed even a single megabyte with an e-book. Some of the largest e-books I own are around 1mb, and those are books that print out to 1,000 pages in paper. So in most cases, oversized e-books are inflicted with oversized graphic files. I would go through all of your images and make sure they are 72 DPI and no larger than 600 pixels wide and/or 800 pixels tall (for images that need to take up the entire width or height of a standard sized e-reader; many illustrations will not need to be that big). Some day these standards may change, as high resolution displays become cheaper, but for now the vast majority of people are using smart phones or e-ink to read books and you just do not need that many pixels to get an image across in those platforms.