Hi The 'zoom' effect you have got will be (most probably) because of the setting in the Personalization window.
So, go back to Personalization window (Right click on desktop), look at the bottom of the window and you should see your picture towards the left, with 'Desktop Background' in blue. Click on this then, again, bottom left you will see 'Picture Position'. Choose either Fit or Fill and see if either of them suit you. You have most likely got it currently on Tile or Centre.
Hope this helps you?