If you would like to override the image scale size for any layer in your timeline, you can optionally do this for any layer by clicking any layer's Settings icon button in the main timeline to open the layer settings, and entering your custom CSS class name into the Optionally include custom CSS classes to this layer in HTML exports input field.

This will ensure that your layer will include your specified custom CSS class name to its HTML class attribute when they're exported to HTML from the Bannerify plugin.