You're building a line-follower, right? So it will drive the motors as required to keep the line-sensor positioned above the line. It doesn't matter that it cannot drive straight on its own.
(I love the "Ardulno Sensor Shield" in the photos. Somehow these guys can sleep better at night if they use Photoshop to change a few pixels in an image and dream that they didn't copy it. I bet their copy of Photoshop is pirated too.)