You will never get the steering to center back to the same point each and every time you move the steering on the controller. Without the Hudy gauges on the car, you would have never known this. As long as it reads .5-degrees out on both sides when setting it, or 0-degree and 1-degree, it makes no difference, you still have .5-degree out.
The tolerances in every single part, including the servo, EVEN BRAND NEW, all introduce a little slop. If you have have .5-degree of slop, you are in excellent shape.
Even if you get your car perfect on the board, once your car is on the track, you can still expect to have to adjust the steering trim to get the car to drive straight. By the end of a race, your Left and Right Front tires will likely be different diameters, which will introduce pull to the left or right again anyway, so just make sure you Toe is how you want closest to center on the servo and transmitter, and then adjust the rest with steering trim.
Now STOP over analyzing it, and go have fun Racing....