arekkorzeniowski You can add a bit custom CSS for it.
On edit screen of that page >> add an extra class for the block you just added:
Then go to template of JA Builder (I guess you're using the same template) >> Custom code and add this custom css:
<style>
@media (max-width: 480px) {
.jub-block.images .col-md-6 {
width: 50%;
float: left;
}
}
</style>
In case that you're using another Joomla template on your site, you can add this code to the custom CSS code section of template:
@media (max-width: 480px) {
.jub-block.images .col-md-6 {
width: 50%;
float: left;
}
}