In Joomla 3.02 there is not the option to align the logo to the center. Here what I have done.
I had this problem and I found a way to center the logo.
I don't know if there are more elegant solutions, here what you can do.
Open the templace css file (templates/protostar/css/template.css) and at the end add the following css class
Maybe you will appreciate this guide found on internet.
and also I am sure you will appreciate the template positions (thanks to Cloud Access)