Integrity means your yes is a yes even when a better offer comes along.

The test of a commitment is what shows up after you make it. Plans agreed on Tuesday get quietly abandoned on Friday, not because anything went wrong, but because a better invitation arrived and nobody says that part out loud. Integrity is treating your earlier yes as binding on your later self. That is the whole difficulty, since the later self never agreed to anything.

Think about the plan you are currently looking for an exit from. Go anyway, and go without making it obvious you are somewhere else in your head. If you truly have to cancel, give the real reason rather than inventing a better one.