We have an 8 week old kitten that uses the litter box sometimes, but most of the time it is on the floor. When she does use the litter box, she does not cover it up. It's like she doesn't know she's a cat! Don't they instinctively want to bury it?
Some cats will not cover it up so do not worry about that. She is a young kitten so give her more time with the litter box. Try a different litter and try another litter box so she has 2 choices. vetcare