your plant grew horizontally because it was stretching towards the light. you do not have anywhere near enough light in there to successfully grow from seedling to harvest. also, you should consider covering your walls with something reflective, such as mylar in order to make the most out of your space. you also need to consider ventilation as well.
it appears as though you are working on a budget. get yourself come CFL's in both warm and cool spectrum. you can use wrapping paper that has a reflective back to it for cheap in place of mylar. you can never have too much light, but you are working with far, far, far, far too little. do some research on this site about minimum lumen requirements per square foot. also, you should not have planted more than one plant in that pot. they will get root bound and kill each other fighting for necessities.
hope this helps