Mars II 400 can cover2.5'x2.5' area,but if you only have one plant so far,it will be enough. But it also depends on which growing method you will use.If you think the light isn't enough,you can add some CFL as side light.
To grow the plant as large as possible you can move the light from one side to the other similarly to how the sun travels
Each half of the plant will get ample time under the light to grow readily. In nature its common to have partial sunny days.
Using a minimum 10 gal container size would help the plant expand to meet your expectations.