Please complete the following steps:
1) Go to the plugin settings page and open "Custom Code" tab.
2) Mark "Activate custom CSS code" checkbox in "CSS" section and insert the following code:
.gallery_box_single {margin: 0 auto; width: 920px;}
You should change the width value based on your specific theme styles and the layout.
3) Save changes.
This article related to Galley by BestWebSoft plugin
Additional resources: Gallery - User Guide
Still need help? Feel free to contact our friendly support team. Create a private ticket