明天我有事情要做。

I have something to do tomorrow?(wrong)

Sorry but I am tied up all day tomorrow.(right)

用I have something to do来表示您很忙，这也完全是中国式的说法。因为每时每刻我们都有事情要做，躺在那里睡大觉也是事情。

所以您可以说我很忙，脱不开身：

I’m tiedup.还有其他的说法：I’m I can’t make it at that time. I’d love to, but I can’t, I have to stay at home.