Annoying pitch changing with audio tracks

Hi,
Received my Mac today, so far loving it.
Started to use garageband, but I'm having a really annoying problem.
No matter what I record, trying to lay down an acoustic guitar track using the macs mic as a test, when I come to play back the track after recording, its always in a different pitch/key. I know garageband wants me to specify I pitch, but I dont want to! Why does it keep trying to change the pitch of the audio Im recording? Its doing it for vocals as well, coming up much lower or higher than what i recorded.
No matter what pitch I try putting the project as, Ive tried all, it NEVER comes up the same as what I originally recorded.
Any help would be great.
Thanks,
Christian