The one thing to know about OpenCart
OpenCart placement is controlled by layouts, not by the widget. If it appears on the wrong pages, change the module assignment in Design rather than rebuilding it.
Where reviews belong on a OpenCart site
Assign the module to the home layout for broad social proof or to selected category and information layouts for more focused placement.
Full-width sections suit carousel and grid layouts; narrow areas suit a badge.
Reviews and search results
The widget outputs review schema markup automatically. Whether Google shows a star rating depends on what the reviews are attached to — worth reading before you expect stars, because for a business reviewing itself the answer is usually no.
What does help either way: reviews on the page are content, and a page that answers what customers actually say is a page people stay on.