Will my plants be root bound from pot not being big enough?

Unfortunately, yes, they will no doubt be root bound by harvest time. I don't see how there is anything you can do about it, apart from transplanting, which I gather is not going to happen. The only thing you must do in this situation, is to be on your toes when it comes to keeping the pots moist and with feeding too. Big plants will require far more frequent watering and an increase in feeding frequency. I would suggest feeding more often, but with a weaker nutrient solution, this way the giant ball of roots and your big plants, are not subjected to high concentrations of nutrients which can burn, while at the same time being under slight moisture stress due to being root bound, with little room left in the substrate to actually hold moisture reserves. In future, if this situation concerns you, you will either have to grow fewer plants in bigger pots, or stay with the same sized pots, but them give less time in veg. Your plants and harvest should be jut fine, as long as you can meet their water and nutrient requirements. Mandala Seeds have an excellent article on their site as to how they "stress test" their plants, growing them in very small containers or with nutrient excesses/deficiencies and this may help alleviate your fears as to what cannabis plants are able to achieve, even if terribly root bound or mistreated with nutrients. They also have many wonderful growing tips, told in a no nonsense style, and I can highly recommend it as being rather informative and full of facts, with no myths or imagined theories. Good luck and happy harvest! Hope this helps,..... Organoman.