Sorry
I’m very sorry
I’m awfully sorry
I’m terribly sorry
I’m extremely sorry

Excuse me
Excuse me for a moment
Excuse me for interrupting

Sorry to have kept you waiting
Sorry to have troubled you
Sorry for being late
I must apologize to you for giving you so much trouble

I’m afraid I have taken up much of your time
I’m afraid I won’t be free this afternoon. Can you make it some other time？