Technically, all cannabis is sativa. So, just jot that down real quick. It's a plant that evolved a bunch of different ways due to the climates the plant was brought to and adapted at. The true specification of cannabis should be broad-leaf and narrow-leaf, but bro science keeps stomping out actual science on that front.
Anyway.
You can always SCrog whenever you want. The question is, will you get much out of SCROGing for it to be worth it. Since there aren't many branches, you'll have to keep it in veg for a few weeks after you SCrog, but that's not a big deal.
Maybe try feeding it more? I don't know about the cultivar you're growing or if it is supposed to be lanky, but do a little research and find out the best way to let it grow.
I hope this helps. Good luck!