With the plane upright it is totally normal to have the center line offset. Looking at the plane from the front ,,,the offset should be to the right of centerline. This is not always the norm, but I can't think of a single plane I've built that didn't line up that way.
Many reasons for this. One simple reason is the built in right thrust of the firewall to compensate the torque effect. If you mounted the engine directly in the center of the firewall the prop shaft would never line up with the spinner hole in the cowling.