In bad lighting my hornwort shed all its needles and didn't really recover. In nice lighting I have a combined 4 feet of bushy hornwort at least. Huge difference in my experience anyway.
i've heard hornwort is not the easiest plant to grow either.. at least it doesn't take well to less than optimal conditions....i had some and it died as well.
try java moss or crypts
Yeah I believe hornwort requires a "high" ammount of lighting.
Java moss and java fern are good low-light plants, you might try one of them depending on the "look" you're going for. I have Java fern in my betta's tanks and they seem to like swimming between the leaves.