My bad! (6)
'my bad' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oops that I've seen before include "Harem" , "Exclamation on making minor error" , "I've messed up" , "Oh dear, that's a mistake!" , "Oh dear, that was careless!" .)
(Other definitions for whoops that I've seen before include "Worrying cry" , "Yikes, I've dropped something!" , "Something said after minor accident or mistake" , "Oh dear! That was a mistake!" , "Loud cries of excitement" .)