Get into a somewhat normal pot first or add soil. ( Is that a bag wrapped around the bottom ? )
Get the light closer.
Stop overwatering.
Do you have any air on it ? You need branch strength and a lot of it when topping.
I'd do all the above first...give it a week or two then think about topping.
IMHO your plant is not shape for topping yet.
Patience is a virtue...
Correcting grow conditions and waiting a couple of weeks can ( and would ) make a world of difference.
This is a topped Blueberry x Northern Lights two weeks from harvest ( Each cola dried / cured to more then oz..easily
)
All buddage in this pic is one plant.
Topping rules ! I love colas.
Edit. One of the colas is gone as I needed the smoke..lol. trying to find a pic of all 4.