Translation is never exact, and these two languages are particularly far apart (about as far as two Indo-European tongues can be).

Here's an even more idiomatic version:

For I must die; and that evil won't come tomorrow
nor in three days, nor in a month,
but right now I'm among those who are no more.

It will come slowly but surely. The best general tip is to put your poet's hat on when you do the polishing.