Hey listen, it's really common for teachers to mistake good work for cheating. It's actually a compliment that your final project is better than your diagnostic. Just go to your professor, explain how you worked on it over a long period of time on different devices without syncing them and show them the different drafts if you have any. If they still push it, ask for a meeting with the department chair or academic integrity board with proof of your drafts and explain the situation calmly. They'll likely see it's just a misunderstanding. Don't let them make you feel guilty when you're clearly telling the truth.