[Plugin: NextGEN Gallery] fitting thumbnails across page

I didn’t get exactly what you mean but you want more than 2 columns of images (in thumbnails), possibly 6? Is that it? If so, go to the Options, Gallery inside the NG config tab and change the “number of columns” from 0 to how many columns you need/want. Have in mind though that the space of the “content” block (where the gallery thumbnails will be displayed) can limit this, for example if you have 400px for the content and you want to have 3 columns with 3 images of say 150px wide each – it will display just the first two and the 3rd will go below these.

Instead if you want more rows, the number of rows of course will be determined according to the number of columns you’ve set and the number of images in the gallery.