I agree I am currently in the process of flowering Liberty Haze and two of the plants got so big they out grew my lights absolutely a lot of sativa in these genetics. I was able to save three of the five and they are coming along nicely though.
That is a pretty small box you have there I would recommend starting in a closet and using an HID light even if its just a small 250W. I would recommend picking up a book from your local book store and reading up on how to grow with that little of light your clone will most likely stretch a lot...