As someone who grows a lot of Sativa plants, gentle feeding is best.
Half strength usually works just fine, but quarter strength twice as often seems to be best.
They seem to like mild feeds often rather than big feeds less often.
you can still get very good yields from plants that don't produce HUGE colas. It will thikcen up.. give it time.
Might want to wire some of that plant together or otherwise support it.. in a few weeks it may not support the weight.