Top it soon if you want to control it without dealing with the main stem.... It's much harder to deal with, and the stem is easy to break... Everything that comes through the screen is directed away from the center... The center gits filled as needed by other growth coming off other branches....
I would for example cut/paste Scottys cleaned out under screen pic, but it seems too much like stealing just to help people avoid reading.... Google: Pineapple express g-13 labs seed to harvest:.... Plus i think it's funny to give the uninformed [not you tucker] required reading to get a clearer look what a Master scroger did... I'm just walking in the shadow of my betters with this grow...
My screen is at 8", the plant was right at the screen when i set it... You gotta pull them back under the screen to get a proper Scottyballs scrog... Since you haven't topped it before, i'd set your screen 2" higher than the newly topped plant... as long as you can work under the screen it's all good,,, We're not trying to grow big trees here... More like really spread out little Bonsai trees.. Keep on veging and pulling'em back down as they grow through...
I would have set my screen higher if i had known she would stretch so much... I did cut new longer screen supports so i can move the screen up a few inches.... Veg yours longer if need be.. Set the screen and keep veging... My plant leaned because it was easier for the plant, the hydroton let it lean by giving a little....
First time out it's easy to over think this... Just follow our leader... It may take a few times to get it perfect..... Scroging is not a bad cult to belong to, no matter what your light source...