Lucy isn't really trying to do magic. She's just sketching out a possible way summoning things directly from the void could work, if one were doing that, instead of asking one's wall for them. Anything worth trying to retrieve from the void that her wall wouldn't give her would probably be a bad idea to bring into the school anyway, at least in terms of things she knows are in the void. Plus her wall might feel slighted, and that would be a shame.
She hasn't put any mana in, when she finishes the circle. Nothing is supposed to happen.