Can't you postpone or cancel the screening? I think most people understand that creative projects can't always follow deadlines. Everyone has a few projects that turn bad even the most successful and talented individuals out there. It's not the end of the world. There will be other opportunities for you. You know what you're capable of, don't let the criticism tell you otherwise. Perhaps, you can take some time away, do other things with your life and come back to it later. Also, don't forget that some people are late bloomers. Please take care of yourself.

Just push through. Don't let your fears get in the way! Think how great it will be once it's complete and awesome!