Can't find the iTunes checkout "cart"
I intended to purchase a tune, but I accidentally clicked the item just below the one I wanted. I tried to find a "cart" that I expected would allow me to buy or to delete the item. No luck. How do I cancel the mistaken purchase and how do I complete a correct purchase? This seems to be such an elementary thing, but it appears to be very strange compared to other sales sites by other companies.
iPhone 4S, iOS 7.0.4, MacPro early 2008, OSX 10.8.5