Once inside, I can't move and that's wrong (7)
I believe the answer is:
inexact
'that's wrong' is the definition.
(thesaurus)
'once inside i can't move' is the wordplay.
'once' becomes 'ex'.
'inside' is an insertion indicator.
'move' indicates an anagram.
'i'+'cant'='icant'
'icant' anagrammed gives 'inact'.
'ex' inserted inside 'inact' is 'INEXACT'.
'and' is the link.
(Other definitions for inexact that I've seen before include "Wide of the mark" , "Not quite accurate" , "Not entirely accurate" , "not precisely correct" , "Lax" .)