Rascal not beginning to make mistake (5)
I believe the answer is:
error
'mistake' is the definition.
(I know that mistake can be written as error)
'rascal not beginning' is the wordplay.
'rascal' becomes 'terror' (terror is a kind of rascal).
'not beginning' means to remove the first letter.
'terror' with its first letter removed is 'ERROR'.
'to make' acts as a link.
(Other definitions for error that I've seen before include "wrong" , "Howler" , "Solecism" , "Trial and ___" , "Faulty judgement" .)