Sampson,

You used kindle previewer to convert to mobi, previewer adds the original epub file into the mobi, so you have a mobi 7, kf8 and epub file altogether, increases the size. Sometimes it doubles it, other times it only adds slightly more. When you submit it to kindle though, they strip out the epub file, so size shouldn’t even be a problem. I’ve uploaded 400mb ebooks via kdp to amazon, works just fine, but it will take a while on amazon’s size to accept the upload and for it to go through.