Timing Belt Alignment Issue

[twins4406]

I'm Installing my 2nd Gate Timing Belt Kit TCKWP335 due to the 60k its the kit with Waterpump Idler & Tensioner. What issue I'm having is when I set the tension on the belt & line up everything up & start the car the belt walks towards the back of the cam pulleys about 1/8 inch. I have tried removing & installing it about a dozen times. I was just wondering if anyone ever had this issue..
Thanks
Jake