Thank you for reaching out for help! Also, an AP class go you!!!!
As a teacher I would recommend the following sites for study.
Here is a great one for study notes and flashcards:
Here a practice test:
and a great blog that covers what to expect from the exam:
cassandra recommends the following next steps:
I can't say which ones are included on the exam itself, but I googled "Landmark Supreme Court Cases," which provided a list of what are generally regarded as the most important cases in the history of the Supreme Court. Studying the cases on this list, their historical context, and how the Court's ruling affected the country would be a great place to start.