I'm awfull/terribly sorry.
I feel really bad about…
I beg your pardon for…
I owe you an apology.
I'm awfully sorry for the other day.
Please accept my apology.
Will you ever forgive me?
May I ask for your forgiveness?
I'm sorry. I quite forgot.
I'm sorry. I forgot all about it.
It was most thoughtless of me.我太粗心了。
Sorry, it slipped my mind.
Please forgive my rudeness.
I'm sorry for my rudeness.
I'm sorry I was rude.
I should have thought of that a long time ago.
It could be better if I had thought of that earlier.
It was careless of me not to find it out.
Oh, how I wish I could find it out earlier.
If only I could put the clock back.
It's all right.
Not in the least.无所谓。
Not a bit of it.一点儿也没什么。
That's not a big deal.没什么大不了。