I see you are using custom purchase-button images on your page; the top of this help page explains how to modify our standard button codes to replace the default button image with a custom one, in a way which should preserve our normal cart functioning and eliminate the Go Back button problem:
If you do it that way and also add at least one complete block of your View Cart code from Seller Admin on every page with any number of Add to Carts (or if you install the WordPress plugin from http://wpejunkie.com/), the cart will appear as an overlay "inside" your own page. Even if you don't add the View Cart code or plugin, the Add to Cart buttons should still fallback to opening the cart in a separate window/tab, with a Continue Shopping (rather than Go Back) button that simply closes that window/tab.
The Go Back button is a fallback to a fallback behavior: if the button cannot open the cart overlay inside your page and cannot open the cart in a separate window/tab, it will simply take the buyer to the cart in the same window as your site, acting just like a normal link. Unfortunately, this method means the cart can't tell which URL the buyer should be returned to, so we have to use a somewhat clumsy Go Back button that simply steps backward in the browser history, just like the browser's own Back button.