I was just fired from my job?

You only missed work once on accident and they fired you? Are you sure that's the only reason? If that really is the only reason, it's an honest mistake. You're 17 and sometime, especially when you're young, you do things like misread a schedule. But if you weren't doing your best or if you blew off work, you need to start trying harder. Either way, I hope everything ends up okay for you. You made a mistake. Lesson learned.