I think there's a nuance between scared and afraid, especially with "I'm not". Ngram Viewer shows that the "not afraid" is used much more that "not scared".
It could be because afraid is more literary and sounds better in books, and Ngram searches books. But I think that:
I'm not scared refers to something specific, scary right now or that has just happened.
I'm not afraid refers to what is coming, what could be scary ahead.
Am I correct?
As I excepted, there are quite a lot of questions about "afraid" vs "scared", but unfortunately most of them are unanswered and none answer my question.