Not happy at this hour! My professor flagged my entire final essay as 88% AI-generated. I wrote every word myself. What do I do?

I just got my grade back for my senior seminar paper, and my professor gave me a zero with a note saying Turnitin flagged it as 88% AI-generated. I did NOT use ChatGPT or any AI tool to write this paper. I wrote it over three weeks in Google Docs and have my complete edit history showing sentence-by-sentence revisions. I emailed my professor offering to share the version history and my draft notes, but she replied saying "the detection software is reliable and the zero stands unless the department head intervenes." Am I completely at the mercy of broken AI detectors?