You can train your plant to do whatever you want with a screen and some twisty ties.

Or you could get the correct light in there. I assume your K (color temperature) of your bulbs is 2700. This is for budding not vegging. Reddish light such as this makes your plants (in general) grow taller with less branches. Bluish light, like you should be using for vegging (about 5700K) tends to make shorter plants with more branching and undergrowth.