when doing this kind of transplanting youll want to make sure to loosen up the pre developed root mass in order for the roots to break out of the form they have already achieved, thus letting new root growth develop within the new soil you have added.
although you didnt do anything wrong, transplanting can sometimes cause shock of sorts and be detrimental to your harvest.
im a believer in starting seeds/clones in small peat type pots where the roots are allowed to grow right through the pot. what this does is eliminates transplant shock because you plant the entire peat pot into the new larger home.
as i was once told by my mentor, "i believe in starting a plant in its LIFE LONG pot"
as far as nutes go. your plant is looking healthy to me. plus new soil holds its own nutes within, but i would start with a mild nute solution (250-400ppm) and see what effect it has on your baby.
hope any of this helps.