Disable Responsible Layout

I don't see any responsive layout for HikaShop on your website.
Note that the responsive layout of hikaShop is only available for Joomla 3.0 and would actually help solve your display issue by switching to a 1 colonne listing automatically on smartphones.

You could have something similar with CSS like that:
@media only screen and (max-width: 800px) {
#hikashop_category_information_menu_102 div.hikashop_category, #hikashop_category_information_menu_102 div.hikashop_product {
width: 100% !important;
}
}

It's you template which squeeze the main content area. And since HikaShop is not responsive on Joomla 2.5, it still displays the products on several columns and doesn't have even space on a line so it displays like that.