To disable the automatic gallery feature, go to Settings > Media and find the Autogallery option. Set it to Disabled.
But if you want to keep the gallery feature on a per-post basis, meaning that images within the same post are grouped together but not include images from other posts on the same archive page, then you need to choose the option Galleries per Section. After that, you need to define the sections below, so they match your themes template. By default, the plugin uses “article” and “div.hentry” because that are the most commonly used identifiers in modern WordPress themes but your theme might use completely different identifiers.
If you can provide a link to your archive page, I can tell you more 🙂