everyone is sure man. they need to have their leaves out of water a bit.. by a bit i ean at least half the leavs out a few inches.. petco also sells bamboo as aquatic and its NOT :P it also is simi aquatic. same with the umbrella plants, pecock ferns and a few other plants :C
You could always put them in a container of water in a sunny window, give them a couple weeks, if they're alive that's good.
You don't want them to die in the tank, dying/dead plants add ammonia to the tank.
teeny is correct :P you can use jars, even plastic bottles with substrate in them to lift them up out of the water and keep them in there if you prefer [tho itd prob look weird but im sure itd help] iv seen ppl use pepsi bottles to do it [tho they prob shoulda took the pepsi logo off lol]
(goes to remove peacock fern from one of her tanks)
I'd bought some bamboo from a petco as well, but luckily I looked up how to plant it on the way home, and realized that it wasn't fully aquatic, so I took it back the next day and they let me exchange it.
Is there a sticky somewhere with a list of recommended fully aquatic tank plants for bettas? That would be wonderfully helpful.