‘You’re awful! You’re terrible! Stupid mistake!’ (3-3)

I believe the answer is:

boo-boo

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'mistake' is the definition.
(I know that boo-boo is a type of mistake)

I can't explain the remainder of the clue.

(Other definitions for boo-boo that I've seen before include "Mistake" , "Clanger" .)

I've seen this clue in The Guardian.

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