Java moss is not planted... You have to tie it to something. For a carpet effect you will have to use a mesh (like that craft screen stuff available at a hobby store, or hairnets). It has to be pruned, and coaxed to get it to look like you want. With the light you have it will take a long time to achieve the effect.
If you post a wanted to buy ad in the classifieds section here, I am sure someone can ship you some java moss on the cheap. I only keep high light stuff at the moment so I do not have any, or I would send you a clump.