Here's what worked for me.
It's not elegant, but added another set of <div></div> tags around the set that contains the map.
I have a page that contains something like this:
<div id="wagmp_map_1" style="width: 500px; height: 300px;"></div>
Adding the centering command to the original div tag had no effect. I see that you did something similar in your code. This is slightly different but it worked for me.