I am really sorry.
I'm awfully sorry. I didn't realize.
I'm sorry. I didn't mean to hurt your feeling.
I'm terribly sorry about…
I'm very sorry for…
It was most careless of me.
It was really quite unintentional.
It was most careless of me.
It was wrong of me.
I really feel bad about…
How clumsy of me to…
I apologize for…
I can't tell you how sorry I am.
I do apologize about that.
I beg you pardon.
I hope you will pardon me for…
I'm extremely sorry.
May I offer you my sincere apologies for …?
Please forgive me for…
I've got to apologize for…
I'm sorry, it was all my fault.