It's tougher, having heard amiss, to get right (6)
I believe the answer is:
harder
'it's tougher' is the definition.
('hard' can be a synonym of 'tough')
'heard amiss to get right' is the wordplay.
'amiss' indicates anagramming the letters.
'to get right' becomes 'r' (I've seen this in other clues).
'heard' anagrammed gives 'harde'.
'harde'+'r'='HARDER'
'having' is the link.
(Other definitions for harder that I've seen before include "More tough or difficult" , "More solid" .)