How serious are AERs?

I've had an AER against me for prescribing one drug instead of another (very similar sounding name) on an electronic prescribing system. The dose was the within the maximum dose of that drug and I don't think any harm has come to the patient.

I received an email asking for an explanation. I stupidly replied before asking for any advice from here. I said I acknowledge the error and will reflect on it.

Should I have given a more formal statement? Should I have involved MDU? Is this likely to have any consequences? Will I be expected to reflect upon this on my portfolio?

Sorry, first time such a thing has happened to me so a bit freaked out.