Using 2-line staff

I am trying to create a 2-line staff; however, the notes don't seem to lie in the lines and spaces in the normal way. In fact, they seem to be spaced out as if there were a 5-line staff. So, if I put in three ascending notes (A, B, C), they all appear within one space (see example).

What I want is to have them appear in the normal way: A in a space, B on a line, C in a space. Is there some way to do this?

(NB: the ABC sequence is just an example. Actually, I am notating chant.)