I was busy or at work when the attunement began, can we do it again?
No, that is not necessary. The attunement works regardless of if you are busy doing something or asleep. If your reason for wanting it done again anyway is to gain satisfaction or feeling comfortable then I would suggest you sit quietly in meditation and ask yourself why you feel unsure of the attunement reaching you. Trust is something you must develop on the way to being an awesome Reiki Master so this is actually an opportunity for you to work on your trust issues.