I am new to growing as well, have similar setup except mine was from seed. You should paint the inside of the box white, this will reflect light better onto your plant. I've heard some people use foil to better effect but I am not really in position to advise you to do so since I've read others complaining about the rise in temperature and creation of hot spots.

How long ago was the clone rooted? Those leaves dont look too good you been giving it nutes? My knowledge on nutes and soil is basic at best so hopefully some one who knows what they are talking about can advise you there.

Good luck with the grow.