「我先走了」的英语并不是说 I go first，「我先离开，非走不可」的英语句要如何表达 呢？

I've got to go.

我得马上走了。 I'd better be going. 我想我该走了。

I must be off now.

我该走了。

I must get going now. I've got an appointment at 5 o'clock.

我得走了，我五点钟有约会。

Got to be going, I'm afraid, or I'll be late at the office.

我该走了，不然上班会迟到。