Can I add more sand to cycling tank?

I have a 12g JBJ Nano Cube and added a 10lb bag of LS (I think it was CaribSea,
not sure since I'm at work, I can find out later if needed). Since the tank
has now been cycling for a week, it has given me a chance to read more. I've
found that some people recommend 3-4 inches of sand substrate on the bottom,
right now I have maybe an inch, less in shallow spots.

My question is, should I add another 10lb? It seems like it would push the
depth to about 2-3 inches. Also, is it ok to add sand this late into cycle?

Thanks for you guidance,
~John