Harry can just claim to have already used it that day for an innocuous purpose, like studying or something. Sure, McGonagall could accuse him of stupidity because that leaves him unprepared for an emergency, but pleading guilty to stupidity is easy. (Well, easier, anyway.)
Harry can just claim to have already used it that day for an innocuous purpose, like studying or something. Sure, McGonagall could accuse him of stupidity because that leaves him unprepared for an emergency, but pleading guilty to stupidity is easy. (Well, easier, anyway.)