Plant overgrowing in grow cabinet

[weedman87]

hi there i have a mj plant 3 weeks into flowering and its already half the height of the grow box i may have let it grow to high in veg the dimensions of the grow box are 2 ft long, 1 ft wide, 4 ft tall in the shape of a rectangle.

will i have to top it or modify the base its sitting on or both

its just going crazy under 3 18 watt fluro tubes 2 3000k 1 6500k

and its on half strength solution

any quierys dont hesitate to ask i may have left some info out .

thanks heaps