have another guess coming
Also, have another think coming. Be mistaken and therefore have to reconsider or rethink one's answer. For example, If you think you can fool me, you have another guess coming, or John thinks he convinced me; well, he has another think coming. A related idiom is guess again, often used in the imperative, as in You think that car cost $20,000? Guess again! [Colloquial; first half of 1900s]