How do you know if your wheel is correctly centered?
If your brakes are rubbing, or the wheel is rubbing on the frame then you probably need to adjust the wheel or the brakes.

The quickest way to check is to use the brakes.

1) Pull the brake lever for the front wheel as far to the handlebar as it will go. It should be at least a finger width from the bar at full compression.

2) While watching the brake pads, the part of the brake touching the wheel, let up slowly on the lever until the pads are almost touching the wheel but not quite.

3) The pads should both be clear of the wheel. If one come clear first then either the brake needs adjusted or the wheel is not centered in the frame.

4) If both brakes clear the wheel at the same time then start turning the wheel slowly while continuing to hold the brake just clear of the wheel. If there's a problem with the wheel one side or the other will hit a brake pad.

You can take it to a shop if the wheel needs to be trued.