Show I cut main stem?

No, since you already flipped the light schedule to flower. You can top and mainline during vegetative growth, but during flower, it's generally not a good idea. It causes stress to the plants and during flower this can result in herming or other unwanted results including reduced yield. In this phase, I'd prefer low stress training. Just bend the main stem using some kind of wire. Supercropping is a valid option also, but as with topping, supercropping can also cause stress. I'd only supercrop during flower if there's no other option. Looking at your photo's, I think bending the higher branches down is the best way to go. You're plant is open and at the higher parts the plant is probably still flexible. So bending those high tops down is the easiest and less stressfull way to achieve a flat canopy imo.