I'm not entirely sure what you're saying, so forgive me if I'm answering the wrong question. First, prose is, in it's simplest definition, writing that isn't poetry, so anything in the fiction categories would count as prose. If you want to break your story into chapters, by all means do so ... especially if you're entering in the novella category. I mean, if you're doing mini fiction, it's unlikely you'll NEED to due to the length (or lack thereof) of stories in that category, but there's nothing wrong with doing it anyway.
If you're referring to wasting your own time, I apologize if I've answered unnecessarily. If you're referring to wasting mine, don't worry; I'm happy to answer any questions or make any clarifications.
If uh... for example...
I submitted an entry of a fiction-categorized story.
Is it alright to use chapter-division? (I'm just getting the difference between prose and fiction-categorized stories)
YES: Don't post already, I know I've wasted enough time.
NO: Please notify...