Keeping polycord on track

[Grim Tuesday]

For our collector, we are using a polycord based system on PVC rollers. Because the PVC is not sticky enough, we are using silicon caulk in between our pulleys. Our system relies on bent aluminium rails to push the ball to the center and the section that rises it to the shooter. However, when the ball enters off center, it pushes the polycord off, as seen in the picture. We tried adding some flat belting, but it only exaggerated the problem, getting more pushed off than the polycord. We don't have a terrible lot of experience with polycord, so I would be very appreciative if someone could point us in the right direction.