Hello Stephen,
The fence reads the scale from a window on the right side of the fence. There should be a pointer on that window. That's why the scale is offset. You don't measure with the fence. You measure through the window on the fence.

I would check the accuracy by measuring between the blade and fence to be sure. Also turn that blade insert around. Looks like they have one side with a wide gap for dadoes and the other side with a narrow gap. You want the least ammount of clearance around the blade so it doesn't pull the strips into the hole when you make the final part of the cut. Once the strip separates the blade wants to pull it down and back.

NEVER put your hands behind the blade. If it kicks back it will take your hand with it and throw your hand into the blade. (Voice of experience).

Usually a rental shop has a foreman to go over the basics of the tool. They should have walked you through setting up the saw. It would be a good idea to ask for a walk-through.