Surprisingly, it's not a problem at all. The fuzzy surface helps to conceal a multitude of potential problems. My own green screen usually features a seam right down the middle and I've never had a problem with it.

Light up the green screen as you would a piece of art: Lights off the side, pointing toward the far side of the screen. That way the crossing lights will evenly light up the whole screen. Two Tota lights easily light up a 10-foot-wide background within 1/4 to 1/3 stop.