It's a type of H. corymbosa, but yes, it's the 'angustifolia'. There is a species H. angustifolia as well, but that's not what you have.
http://www.aquaticplantcentral.com/...s.php?id=139&category=family&spec=Acanthaceae
http://www.aquaticplantcentral.com/...s.php?id=139&category=family&spec=Acanthaceae