If your goal is to be best buddies, then you did fine. If your goal is to win her back, then you were better off not even calling her back.
I thought you were going to do NC? The rules of no contact are pretty simple. IF she calls you do not answer. You are busy, remember? If it is important she will leave a message. Or followup with a text. If she does either, the rules for responding is to ONLY respond to direct questions via text. But then in your own time (not right away) and in as few words as possible. Yes or no questions get yes or no answers.
Walkaways often want to keep their ex around as BFFs. I am assuming you want to avoid the friend-zone.
Hm yeah, I just feel it's a bit douche when we said that about this important subject we will communicate - in the end we are just humans as well no?