If I were almost finished with a project on a tight deadline when I realized I'd made a mistake back in the beginning that required me to start over, I would take a deep breath and assess the situation. I would then prioritize the tasks that need to be completed and determine which ones can be done quickly and which ones will take more time. I would then create a timeline for completing the project and break it down into manageable chunks. I would also reach out to my team or supervisor for help if needed. Finally, I would stay focused and motivated to complete the project on time.