To finish a short fictional story, you need to have a well-defined conclusion in mind. Consider the themes and character arcs you've developed and bring them to a natural close. Also, pay attention to the language and style, making it consistent and engaging throughout.
Finishing a short fictional story can be done by thinking about what message or emotion you want to leave the reader with. Build towards that, and don't introduce new elements at the end that confuse the story. Keep it concise and impactful.