Yield is determined on Lights/ing, Nutes, etc.. It looks fine to me, my friend's lowryder is about that size and is only 4 weeks into veg. IMHO I would find a wider space, that looks a little narrow, and you can see the leaves resting against the back of your box. Otherwise it looks great, and hope for female.

I have read, and heard that when doing the 12/12 cycle, for 1 hour have your timer turn on the lights, and there is a better chance it will be Female.

What Nutes are you using?

One last thing, when its time to harvest, the "Wet Buds" Might way a lot, but guaranteed its going to weigh 75% less.