Is the math in aerospace engineering hard?

Thank you for your interesting question. University-level math is one step more advanced than high school math but remember, each of us has our own ways of learning and progressing to and through that stage. For now, to help you assess where you stand in the learning process I can think of several possibilities. First, take advantage of whatever home school forums and experiences you can, to reassure yourself that you on-track with the level of understanding needed for a junior in high school. There may also be extra on-line or small group challenges that you can make use of to improve your understanding and confidence. Second, even when you are teaching yourself, there are all kinds of on-line "lectures" that might help you grasp some of the more challenging aspects of whatever your learning topic happens to be. Perhaps even more formalized distance learning could be considered. When you are ready, remember that many universities offer a "refresher" course for math before the regular term starts. Also, most universities have tutorial sessions or problem analysis sessions with teaching assistants to supplement the lectures and/or on-line portions of the course. These tutorial sessions are, for many, essential to success. I wish you all the best in achieving your goal.