The first time I did a timing belt in the engine bay I used one of those plastic things for the cams. I had the same problem: no matter how "lined up" everything was when I put the belt on, once it was tensioned something was off. It's because the portion of the belt between the cams and crank on the idler side is not tensioned when you put it on, and when you tension it, it pulls them out of line. I solved it by retarding the crank one tooth when I laid the belt on; it all lined up when tensioned.

The next time I did a belt in car, I left the plastic thing in my toolbox and used a method similar to Reza's. It went much more quickly.

Either way, glad you sorted your problem. Now get that Mobil 1 out of your engine, put some conventional back in, and GO BREAK HER IN!! I know you've heard mixed reviews on break-in period but anybody who thinks your engine is broken in with less than 50mi on the clock is out of their freaking mind.