Hi there this happens on our site too. I use the below CSS to hide the sidebar below the tablet width of 1024px:
@media (max-width: 1024px) {
#left-sidebar {
display: none;
}
}
It hides the sidebar but the main content of the shop page still only occupies 75% of the screen. See below example page, shrink the browser and you can see there is a point at which the side bar disappears but the products do not expand fully to 100% until the page gets a bit smaller.
https://www.supereight.net/shop/