There’s a difference between ACR guidelines, what you should do, and what you do to keep from getting in trouble.
Trouble wise you’re safe. A nothingburger that would have reared its head already if it had consequences.
In terms of what you should do, I don’t think anything of harm could reasonably befall the patient, so in terms of nonmaleficence and beneficence I think you’re square.
The ACR bean counters would expect you to addend and call the provider.
Personally if I were faced with the circumstances I think I’d leave it be. Again I don’t think future harm is conceivable, and letting the doc know and changing the report might freak the patient out unnecessarily.