Go back, turn back, turn around. All express this better than the given "walk back"
Go back or walk towards the back are okay, but turn around is unacceptable as a translation for this sentence, especially without the appropriate context.
I'LL BE BACK!
"Walk back" is ok in the context that you know it is a command.
For general context is should be "To walk back."
does this mean "walk back" as in walk backwards or just walk back to where you came from?
Walk back was marked as an incorrect translation for 往后 走 in a chinese to English exercise earlier, there it required us to say walk to the back.
往回走 might be a better translation here.
靠后走 was rejected.