Unweighted GPA of 3.97, and ACT of 35. Wow!
That pretty much answers the question. You are very well qualified to attend ND. You did not get in only because of being legacy.
To me your ECs are also very good.
I definitely think that you earned this. Congratulations!
Understand that at ND (or any other top school) there will be a lot of very strong students like you. You will need to work hard to keep up. However, you will also find more people who are potential “like you” colleagues, and you will get a great education.