Just tie her down just be careful all you need is a nail or a screw on the side of your pot and some string and tie her down a little and each day go out and tighten it a little more till she is at the height you need hope that helps good luck with your grow
Also if you just started flowering shes going to double in size so make sure you start tieing her down
If you wanted to top should of done earlier in veg. If you didnt want it so big you should of flipped the lights to 12 12 when it was half that size. Now all you can do is tie it down like the other lads said. Tie it down a lot! its going to do a lot of growing them first few weeks you change the lights over!
IF you can find some sort of cage to put between your lights and the plant, it would prevent your plants from growing into the light and they will use the rest of the space to grow to. Make sure the cage is not small netting, large spacing so the light is not obstructed too much, I am looking into a similar set-up right now. I will update if I find anything useful.
Question, are your light on top only? I have a side strip to help with lighting the bottom of the plant. I'm going to attempt the same technique but need to be crafty
Been there lol. First grow filled the room! Finally started to tie over but broke every stem! Actually the plants (White Russian) were ok and thrived, wouldnt recommend the breaking though!