It is not a moss, it is actually in the fern family~
It is also called susswassertang <although you can sometimes see it as subwassertang, but that is incorrect> It was, in the past, confused with Pelia, <a liverwort> but if it feels rigid to the touch <almost like plastic film> that is what it is. You can tie it down like you did and it will fill up. It is a rare and pretty plant. I have some to :dance2:
A friend of a friend ID'd this .... susswassertang is what it is called.
It takes a while...loves light and CO2.
Keep it ited down. It will attach over time.