Hey dude I gotta say you are not rootbound at all you just didn't give her enough N in the begining and she's eaten all of it up... I grow plants in 20oz bottles under CFL's and they finish at 14-17" tall yielding 7-14g dry each so it's all in how you feed em bro...
Not trying to hijack but I thought I would give you a idea of what you may get from you plant cuz it reminds me of my first grow and I used a 2 liter bottle with the top cut off for my container I did LST on it and I got 14.2g dry from her of some primo bud...
p.s wait it out bro cuz I was stupid and brought mine down at 8 weeks and if I would have let it go to 9 1/2 or 10weeks I would've seen it turn purple like the last pic which I will be harvesting in a week from today and it's 17" tall in a 20oz bottle so root bound is a state of mind to me since I learned my methods from DrBud
Not trying to hijack just thought yo might like to see a similar plant and it looks like yours may be a little bigger than mine was so you probably have a 1/2 oz coming to you of some wonderful smoke