Oftentimes when this happens, multiples of courses or products have been added to the cart. 

You can adjust the quantity of items in your cart by clicking "View cart" at the top left of the page. Once you are in the cart, look for "Quantity" in the green bar at the top of your order. Underneath that will show the quantity of items. Click the up and down arrows next to the number to adjust the amount. If you have any trouble with the arrows, you can highlight the number and type in "1" After you adjust the number, click update cart. 

I have underlined these three places in red in the screenshot below: