Thumbnails show as one column

If i’m not mistaken, you have to adjust that at 2 places

– Gallery -> Gallery Settings -> NextGEN Thumbnails
and then when you have a page with a gallery on it, click at pic and then
– Display Galleries -> Customize the display settings

This might work:

Edit the file /wp-content/ngg_styles/nggallery.css and add this:

.ngg-gallery-thumbnail-box {
    margin-right: 0px;
}