Jonah seemed to repent in chapter two. But is it possible to repent of your repentance? Don’t you and I do that all the time? Have you ever been sorry for your sin only to find yourself doing it again?
In chapter 3, God tells Jonah once again to go to Nineveh. This time he actually does, but it seems like he does the bare minimum required for the job. He barely goes into the city and preaches the only part of God’s message he likes - the part about Nineveh’s destruction. Yet, somehow God still uses Jonah’s actions and brings rescue to the great city of Nineveh. They humble themselves before God and recognize His power over them, and in His graciousness, He saves them.