I have to apologize for a procedural error at work, and am unsure about selecting the right form of apology from the variants of 「ご迷惑をおかけ・・・」:
Also, whether or not to append 「でした」to the end.
The thing I am apologizing for is a mistake in a business purchase. I charged a purchase to my corporate card, but should have had the vendor bill monthly using the 分割払【ぶんかつばら】い option. So a brief explanation, concluding with this apology, will be written in the comment section of my expense report. The reason for apologizing is not to really say I am sorry, but just to let everybody in the approval chain for my expense report know that I now know I did it wrong, and won't do it like this in the future.
I chose to write it as follows:
Firstly, this is an internal company communication, and the people to whom I will submit this document are of a lesser coporate rank than myself (although they are not my subordinates, since the work for the Finance Department). So I felt like 「申し訳ございません」was too much.
(Also, I confess, because I don't yet really understand the full nuance of super-polite self-humbling apology in Japanese, so I tend to never use verbs like 「ございます」or 「いたします」. )
Does that reasoning make sense?
Secondly, as for the 「でした」 at the end, I put it in the past tense because the procedural error I made happened last month. The way I think of it, I'm saying, "Sorry for the error I made last month," so I put it in past tense.
But I wasn't confident about this, because the actual bother I am causing them is actually happening at the time I submit my expense report. So in a different sense I am saying, "Sorry for the bother I am causing you right now by submitting this unexpectedly high expense report, due to the error I made last month". Thought about that way, I wondered if the apology should be in the present tense.
Which is correct? Or might either one work?
(And speaking of apologies: sorry for the two-part question; I couldn't cleanly separate these two concerns.)