Just don't show up at the gate.
If you were to do this on a regular basis, you might get in trouble. Once or twice won't be an issue. I have done this on occasion. I do know that they keep records, but it never became an issue.
If it were clear that you did this by design they might have a case that you are trying to circumvent the conditions. In your case, you bought in good faith but then something happened. Back to McDonalds insisting giving you a discount as long as you eat their junk in its entirety, which obviously makes no sense. They surely would not want to go to court on a case which they cannot win.