Looks like a Jade or Crassula ovata. More specifically a type known as skinny fingers (hopefully that's the correct cultivar).

Most important to its health is get it out of the glass. It needs well draining soil and a pot with a drainage hole, or 3.

It's a terrarium so I was told it was supposed to be in glass and that the plant didn't actually need a lot of sunlight so it didn't need to be near a window. The roots are in soil and moss is packed over it to hold in moisture.

Is it planted wrong?

Also the top layer with the moss has sand in it if that's helpful to add

Not sure where you got your information but sadly, I don't think they could have gotten it more backwards if they tried.

It needs plenty of light but don't just put it directly into sunlight, it will need to be slowly acclimated.

Moss is bad because you don't want the soil holding water. And sand is bad for the same reason, also it can prevent the roots from "breathing" properly.

Aw man, if I take the moss out and allow it to sit in sunlight more will it still have a chance? I'm really hoping I haven't killed it at this point

It has a chance if you repot it. Just taking the moss away & giving it more light - while a step in right direction - is not enough. Drainage has to be addressed, otherwise there is a good chance of plant rotting.

I have to agree with rina. The best bet would be to repot and slowly move it to more and more light. I may get scolded for this next statement but from what I've witnessed, Jades don't require soil that drains AS quickly as most succulents I've seen. But perlite would still be a really good additive for some extra drainage.