You’re fine. MG fiction ranges between 25,000 and 45,000 words. But forget that for now. You need to focus on definitively identifying your audience. You must know your audience in order to write a story that successfully connects with them. Is your topic right for 9- to 12-year-olds? How about your narrative sensibility? That is, does the story express concerns that reflect a middle grader’s way of viewing the world? Kids that age are typically focused inward, struggling to find out who they are. They shouldn’t sound too self-aware by analyzing themselves or others. Let them judge and act quickly — and then face the fallout.