Large white margin on right of products

That is not a sidebar or css issuue you have in your page.
It is an issue of the quantity of products to be displayed in a row.

.woocommerce ul.products li.product, .woocommerce-page ul.products li.product {
  float: left;
  margin: 0 3.8% 2.992em 0;
  padding: 0;
  position: relative;
  width: 22.05%;
}

Your theme has a width of 22.05% which will be suitable for 4 items in a row,
BUT
You have a setting of 3 products to display in row.

After the 3rd product, the 4th one is in the next row;
that is why you have that blank area on the far-right side.

(You can check it by changing that width value to 30% and you will see that 3 products will fill all the width)

If you want to have 3 products in a row, just change the style,
or if yo want to change the quantity of the products to be displayed in a row,
add a proper code snippet to the functions.ph such as described in the Woo-Docs:
https://docs.woothemes.com/document/change-number-of-products-per-row/

Awesome – thank you for your quick response and help.