I would say next time you water do so without food & if it dosen't start looking better in a few days than give a very diluted amout of nutrients - this should help. You seem to have enough room in their for at least two small plants maybe even 3 or 4. You can get seeds that are bred to grow smaller or you could use techniques like LST & supercropping to you advantage. There is also SOG & ScRog but these are a little more complicated.