While in the Customize window, grab a corner of the Flexible Space and move it. Flexible Space, not Space.

I click and drag the flexable space into the toolbar to the left of the URL address text box but can't seeem to change the size of the space that it takes up in the toolbar. When I try to grab the corner when its in the toolbar it just moves rather then allowing me to resize the space it will take up.

It's been a long time, so I am not remembering. Try moving the icons next to the Flexible Space.

Flexible space is flexible and can have any length. You can try this out on the Bookmarks Toolbar left/right if this bar still has empty space to center the bookmarks. The location bar and search bar are more flexible and the length of all flexible elements changes when you resize the window. There is not much you can do about the size of flexible elements although you can change the relative size of the location/search bar container by placing the mouse between the two bars is normal mode.