Cries "I've made a mistake!" (6)
I believe the answer is:
whoops
This clue is a double definition.
'cries' is the first definition.
(whoop is a kind of cry)
'i've made a mistake' is the second definition.
(exclamation acknowledging a mistake)
(Other definitions for whoops that I've seen before include "Loud cries of excitement" , "Worrying cry" , "Exclamation after making a mistake" , "Oh dear! That was a mistake!" , "Exclamation after a mistake; wild cries" .)