If you are in a tent, which I think you are...measure the distance between each pole dimension and subtract 1/4" on both. When you are in the big box store, buy a packet of 12" zip tie's to secure a scrog to the tent poles, use one zip tie wrapped around the pole, tighten it enough so it is loose on the pole and there is room to slip another tie between the pole and tie, slip the next tie between the pole tie and around your scrog corner, once you get it hung in all corners, slowly tighten each tie while you level it, once you have it secured, tighten the tie around the tent pole just enough so you can raise or lower it to where you want it.
Since I have a fixed room, I used the 1"x2" to screw to the 2"x4" stud walls and just set it on top, if you are in a tent you would not need the 1"x2" and my room is 60" wide, so you would need only (2) 8' 2"x 2"s...cheaper yet