You can encourage the plant to grow more outward, by applying some side lighting to areas where you want the plant to reach out.
Sometimes a light placed high above plant can also cause that type of reaching/growth pattern, or if you are running a single weaker light, like a CFL.
Your plant looks nice and green and healthy.
Using blue spectrum lighting will promote vegetation and tighter internode gaps/spacing resulting in a bushier, tighter plant.
The redder spectrums will promote more stretch and draw the branches out more.
If you applied some 2700k CFLs to the sides, it might spread itself out more.
Either way, the plant looks good.
Sometimes your light can cause the plant to keep itself close together to stay in the footprint.
Or....you could just have a weird plant.
Peace and happy growing