Correção: "I'm sorry for notifying..."

I'd like to know if I made any mistakes or if I can improve my passage below in some way.

I'm sorry for notifying you at the last moment, but I'll have to call off the meeting. Something came up at the last minute and I can't postpone it. I'll call you up about the meeting when I'm available.

By the way, is there any difference between "to call" and "to call up"? Is the second one more formal than the first one?