If you place high, you can always take a lower course. Often, this is a good idea. Many students opt to take a review course to build a more solid foundation.
For example, if you place into Calculus (Math 122A+122B), you can take Calculus Preparation (Math 120R) or College Algebra (112) instead.
Please note that once you successfully complete a UA Math course, you will not receive credit for a lower level or prerequisite math course without special permission from the Math Department.