You gotta learn topping for your gro. But its too late now your in flower, so dont bother with it. Your stretch will be done approx in 11 days, because 21 days in flower is when I find the plants stop growing taller. Nothing will happen if you top now.
Yeah, I just got carried away this round and didn't expect the one plant to stretch so much and i I'm at day 11~ so hopefully it is done stretching. 7 plants topped in a 3x3 wouldn't have worked so well either I don't think lol