Happy to be wrong, in my case (5)
I believe the answer is:
merry
'happy' is the definition.
(thesaurus)
'wrong in my case' is the wordplay.
I cannot quite see how this works, but
'wrong' could be 'err' (to err is make an error) and 'err' is found in the answer.
'my' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'to be' is the link.
Can you help me to learn more?
(Other definitions for merry that I've seen before include "Fjull of fun and gaiety" , "Drunk - happy" , "Old King Cole was a ..... old soul" , "Joyous, cheerful" , "Jovial" .)