There's definitely something happening with the upper leaves. If you think that you plant is too high, u must know that it will beg even bigger.
What could help your plant is to cut 30cm from the top branch. That part is burned by the light, and within 3 weeks it will be touching the light.
You will get a bigger wield by sacrificing a part of the plant.
Sativa plants are tall!! hahaa
Wish you a great luck, any question PM me.