Miscalculate in East River twice (3)
I believe the answer is:
err
'miscalculate' is the definition.
(I've seen this before)
'in east river twice' is the wordplay.
'river twice' means two substitutions for 'river'.
'in' says the answer is hidden in the clue.
'ERR' is hidden in the letters of 'east river river'.
(Other definitions for err that I've seen before include "Blunder" , "Sin" , "Be incorrect" , "Drop a clanger" , "Bungle" .)