It's tougher, having heard amiss, to get right (6)
I believe the answer is:
harder
'it's tougher' is the definition.
('hard' is associated in meaning with 'tough')
'heard amiss to get right' is the wordplay.
'amiss' indicates an anagram.
'to get right' becomes 'r' (I've seen this in other clues).
'heard' with letters rearranged 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" .)