You are using the old version which had files all over you had to edit to modify things. The development snapshot contains all the changes I have made to the script since I took over development of it. It includes a centered grid by default and a lot of bug fixes. You may wish to start fresh with it and see if it’s any easier. You can edit the header and footers for it in the html folder.
If you prefer to continue using the current version then there are instructions some place on this site already on how to center the grid.