FYI, Petsmart has a 14 day guarantee on live animals and plants they sell. So yes, you can take the non-aquatic plants back.
I did the same thing actually, I believed the dweeb standing near the fish section when he told me Mondo Grass was fine completely submerged and bought it on an impulse. When I got home and did some research, I realized my mistake, my wife marched into Petsmart, told them off for me (God love her, don't tick her off lol), and exchanged the Mondo Grass for Anacharis. The anacharis is going nuts in my 10 gal and 1.5 gal. I actually took a two inch clipping from a semi-healthy anacharis a few weeks ago and threw it in my 1.5 gal just to see how it would do. It's now six inches long and green as can be.