I'd thought the fit to fly // passenger locator form process for entry to UK proves your vaccination status as its built to allow you Into UK , having gone through the process tat the stadium I would not worry there's not much of a heavy studying of documentation anyways
And I'm sure if you had a friend who had a QR code and he happened to share the image to your phone , a quick flash of it at the entrance should see you in .
Good luck.
Other option email club?