Jillian,
It is okay for students to get the wrong answer, but make sure that you tell them that it is wrong and why it is wrong. Most likely if they got the wrong answer, so did a few others in the class. Let them show you the way that they got the wrong answer, and then show them your way and tell them why that is the correct way to do so. If you don't want them at all to get the wrong answe...