I'm about to run? That must be an error (8)
I believe the answer is:
misprint
'error' is the definition.
(I know that misprint is a type of error)
'i'm about to run?' is the wordplay.
'about' says the letters should be written in reverse.
'to run?' becomes 'sprint' (sprinting is a kind of running).
'im' back-to-front is 'mi'.
'mi'+'sprint'='MISPRINT'
'that must be an' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for misprint that I've seen before include "Type of slip" , "could make sinners of the winners!" , "Possibly the wrong character" , "Typical accident" , "Literal interpretation" .)