Centering galleries

I don’t understand why it is so hard to center a NexGEN gallery. I’ve spent 3 hours thus far trying to center one stupid gallery on my page. From the support pages I’ve been reading, people have been having this problem for FOUR years. What’s up? I have a simple 15-image gallery presented in 3 5-image lines. It left-justifies and nothing will center it. On other sites I’ve just plunked in a gallery, said “center” and center it does. Not so here.

Do I have to take special classes at the university to learn the code allowing me to center my NexGEN gallery? It’s frustrating. Has anyone come up with a solution? Is there a different gallery plug-in that centers easier?

https://www.ads-software.com/plugins/nextgen-gallery/