Noob servo question

[kinggareth]

Sorry for the noob question, but I'm a noob so it's my job.

When mounting the servo horn on my servo i had the servo centred but the horn wouldn't go on pointing straight up it would sit either one way or the other. Now that everything is together I have to run the trim on the steering at 60% to the left to get everything straight.
The problem is that now the car steers significantly tighter to the right than the left which is really noticeable when driving it and is less than ideal.

Is there anyway of re-centring the servo or any other ways around this problem?

EDIT. if it makes any difference, the servo is an absima, the radio gear is Sanwa MT-s and the car is a B6