As a current student at the University of Michigan, I can say that the application process is very holistic. So although a rigorous curriculum may be important, they also look for an upwards trend and extracurriculars that stand out. Essays are extremely important so I would focus more on that rather than worrying too much about the APs that you have or have not taken. I know people with amazing stats that did not get in and those that may not have the best stats get it.