You're right, that scene wasn't in the film from what i can remember.
Don't give up on 3D due to this film though! It wasn't actually filmed in 3D like other, better 3D films like 'Avatar'. It was converted after being filmed like 'Clash of the Titans' (admittedly, the people who converted 'Piranha' did a better job of it though!), hence why the 3D doesn't really look as good as it could have looked.