很遗憾我不能去，星期六我已经有安排了。

Oh, sorry, I can't. I have arranged to visit some friends on Saturday.

youdao

很遗憾，我不能去。

I am very sorry I won't be able to go.

《新英汉大辞典》

我很遗憾告诉你我不能去参加你的生日晚会了。

I regret to tell you that I can't go to your birth-day party.

youdao