It only takes one notch out on the positioning to be noticeable.
...and it only takes moving it one notch/spline to make it out by the same amount but the other side

(I know from having tried this myself in the past).
The offset steering wheel situation is usually caused by someone adjusting the tracking on one side track rod only, rather then adjusting both; usually because they are either bone idle or clueless.
The only way to acheive 'dead-ahead' steering alignment is to ensure that steering wheel is clamped in the straight ahead position, and then adjust the track-rod ends - if the steering wheel is to the left when the wheels are straight ahead, the left hand track rod needs winding in slightly (shortening) and the right hand one needs to be wound out (lengthened) by the same amount. Ideally you either need a tracking alignment tool of some sort to assist with this to ensure that you don't end up upsetting the tracking.
Alternatively, you could just take the car to a garage that does wheel alignment and ask them to adjust the steering wheel to centre. Another option would be to make the adjustment yourself and then take the car for an alignment check to verify that it is OK (don't know about where you are, but in the UK most places will do the initial check for free. The danger here is that if it does need adjusting, they may end up with the steering wheel slightly misaligned again!