I
itsus
you might want to tie the middle of the screen down to your table. when they start to push up, the screen will try to bow upward. try to get her a little more taught too, like fingaz said.
here is a pic of my Scrog right now well about 5 days ago any way. 4 plants I vegged them and never trained them. moved them into the flower room and put the screen on. they are training well and are going to be way to big for this screen, but thats allright I will yield more this way with one light then just doing them bush style. I am wondering about your screen the holes are real big. it looks like the whole plant can fit through one square. Are you going to train them with that screen?