Since this is a deprecated tag anyway, remove it from the output of [-- PREVNEXT --], we can then place the function in a <div> and locate the output left, center, or right using CSS.
If it doesn't work for you, then you probably need to upgrade your version of ShopSite, because I see this option for the PrevNext tag in the Custom Template Spec in the online documentation going back to ShopSite v7.1: