很抱歉英语书面语

I'm so sorry.

i'msorry,sorry希望能帮到你！呵呵

sorry，比如Iamsorry，表示我很抱歉，或者直接用sorry

Dear Betty: I'm so happy to get your Invitation. Thanks ! I really want to go to your Birthday party. But I'm so sorry that I can't go to your birthday party tomorrow , because my mom was ill. I must stay at home and take care of her. Happy birthday,Betty. Have a good time tomorrow. Yours : Tom

对不起是sorry道歉的话是apologize