Val spreads by runners. Is this what you mean when you say, " it has three stems that reach out"? The runners look like thin rods with arrow shaped heads on the end. They come from the crown of the plant, which is the part right above the roots. They will continue to spread these runners forming a sort of chain along the gravel. If you want you can separate the daugter plant from the mother plant once it has grown a decent size. This is a rosette plant, different from a stem plant, that cannot be cut at the leaves and propagated. If a leaf is cut it will most likely rot away, though some people report otherwise. Val grows very long leaves. The smaller type will grow to about 2 feet long. To try and keep it smaller, this is no gaurantee, you can cut of the outer leaves with a sharp kinfe where the leaf meets the base or crown.
Rotala as any stem plant is a fast grower with the proper lighting, CO2, and fertilizers. I have some in a ten gallon with 20 watts of light, diy CO2, and occasional trace ferts so far it is growing pretty quickly. My val, which is in the same tank and about a month old, has sprouted a runner which has grown about 3 inches in a week.
Once the sword out grows your tank you could trade it back to the LFS, though I doubt they would want it. Or you could swap it online at one of the fish/ plant oriented forum. I'm not sure if this site has a page for swaps, but other boards that I frequent do.