Suggestion Box

The genre as it's listed is "Biographical" which can work as both a biography of someone or in the sense of an autobiography, since the word just means pertaining to someone's life. If it were simply "Biography" I could see what you mean with it but as northernwrites pointed out, there are a large number of genres and we can't add everything or it would be overwhelming. Your best solution is to use "Biographical" since it does cover autobiography and then add in the Keywords section that it specifically an autobiography. You can also make sure to say that in the short description of the item, so people who read it would know quickly that it is one.

Hope that helps!