hi at all
in this sentence
I've been on the straight and narrow,
And it's due to come off in a couple of Days.
i founded narrow as adjective not as name so i don't understand the meaning of narrow and of it's due
"the straight and narrow" is an abbreviation for "the straight and narrow path" which is a symbolic term for virtuous behaviour.
"it's due to come off" >> it is scheduled to happen, or just it is scheduled to be removed. Context will tell you which is the right one.