Sagittaria is one possible, but I have less experience with these (they tend not to do well, meaning last long, in my tanks perhaps because of the Helanthium in with them). But Helanthium tenellum or H. bolivianum are two other possibles. And there is the similar micro sword, Lilaeopsis brasiliensis.
It is often difficult to ID plants from the nursery (when you don't have the tag or see the invoice to the store) because they will be grown emersed as opposed to submersed when the plant is amphibious as this plant likely is. The form when grown emersed is strikingly different from that when the plant is grown submersed. This is why you will probably observe as these plants settle in your aquarium that new growth will be somewhat different in leaf shape, size (length and width), and shade of green. That is, if this is either a Sagittaria or Helanthium or Lilaeopsis species.