Can't centre my picture in normal browser mode . It is fine in full screen.

What exactly are you trying to do in the browser? The Viewer should cener the photos, in split screen mode and "Viewer" mode, but the browser will not center the photos, afaik.

Or are you saying the "Viewer" photos are off-center?

This can be caused by a broken preferences file.

Try to remove your user preferences as described in this document : the Apple Aperture trouble-shooting page.

You user library may still be hidden, as is the default in Mavericks: To open your hidden user library:

• Select the "Home" folder icon (the little house) in the Finder's sidebar and press the key combination ⌘J to open the "view options".
• Enable "Show Library Folder".
• Then open the Home folder and open the Library folder inside and navigate to ~/Library/Preferences

These files and folders need removing:

~/Library/Preferences/com.apple.Aperture.plist

~/Library/Containers/com.apple.Aperture

After removing the Preferences files it is essential to log off and on again, or to restart the computer, before you launch Aperture again. Otherwise it may not take effect.

Can you post a couple of screenshots? One off center and the other OK one.

You're welcome 🙂