Hi,
Try it; it will fix the problem:
open this CSS file:
/templates/gk_msocial/html/com_virtuemart/assets/css/flexibleVM2Global.css
and include this CSS rule (to the bottom);
div.FlexibleRelatedProducts.responsive { width:100%;}
By the way, the slider automatically calculates the height of the slider by looking at the product pictures height. But If the "height" is not enough to fit the product titles&pictures (because i am seeing your joomla template uses large pixel value for line-height and the font size is also little large), then you can include this CSS rule below, to manually alter the height of the slider:
div.FlexibleAdditional_wrapper { height:300px !important;}
(Change the pixel value as you wish, try to increase or decrease and find the best value that fits your overall layout)
Regards,
Support