BM Content builder obeys the rule of 12 columns width.
When you add a new module, it’s 12 width cols by default. You could adjust the module width by the tools bar on each module.
The module will be fullwidth if the width is over 12 columns. If you want the 2 or more modules to stay in the same row. Please make sure the width of all modules is less than or equal to 12 columns. Please refer to the video guide (00:19):