First of all, lots of things go into your SAT score, and only some of them are relevant to doing well in college. (You aren’t going to have to take any 4-hour tests at IU, but the ability to sit still and focus for 4 hours is critical to doing well on the SAT). Second of all, your SAT score is good.
College is definitely going to be harder than normal high school classes. I think college classes are roughly comparable to taking accelerated versions of AP classes. You will only spend 2.5 hours a week in class for a typical college class, while you had 4-5 hours in class in high school. Plus, college courses are only 16 weeks maximum, while some high school classes were 36 weeks.
You just have to make up for some of that lost time by studying more outside of class. The good news is that you have a lot more free time than in high school, so you should have plenty of time to study. In high school, you could pretty easily get by with no or very little studying. That’s not going to work in college, so it’s harder in that sense. But if you commit to studying a few hours a day or 2 before each exam (some exams can require a lot more time such as A100), you can do well. You would also be surprised at how many students skip class. Some classes, especially early on, will be half full on some days. Just going to every class will give you a huge advantage over everyone else. As long as you attend every class, complete all assignments, and study for every exam, you should be able to do well.
There’s not much you need to be doing now other than knowing which classes you want to take before orientation. You should be taking a mix of classes that fulfill I-Core prereqs and gen ed requirements in your first semester while considering any AP credits you might bring in:
https://gened.indiana.edu/requirements/index.html
https://admissions.indiana.edu/apply/freshman/ap-exam-credit.html
Use ratemyprofessors.com and see my reply in this thread about how to use the grade distribution database:
There’s not any need to do all of this now, but you can even see actual class times below. Stuff will fill up before you register, so I wouldn’t worry about that too much right now.
https://one.iu.edu/launch-task/iu/igps-plan?terms=igps
It’s also good that you have a healthy fear of failure, but try not to worry about it too much right now. Other than planning a schedule, just try to enjoy the rest of high school. If you manage your time well in college, you’ll be able to do just as well as you are doing in high school while having a lot more free time. I know this is a ton of information, and probably more than you asked for, but let me know if you have any questions. I’m a junior at IU and I’m happy to help you out.