Make an oopsie (4)

I think it could be either:

Which length description are you looking for?:

err

'make an oopsie' is the definition.
(I've seen this in another clue)

This is the entire clue.

(Other definitions for err that I've seen before include "Make mistake in Canberra" , "Go astray" , "Drop a clanger" , "Miss the mark" , "Leave the straight and narrow" .)

I've seen this clue in the Universal.

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