If you are being redirected to the bookstore website than you could be selecting the wrong link, or your instructor has installed an older version of the link.
If the link you are selecting is titled "Purchase Course Materials" then this is not the First Day link. This is a link that will take you to the bookstore website where you can purchase materials.
If the link you are selecting is titled "Course Materials" (or First Day or similar) and is taking you to the bookstore website, then this may be the wrong link. Check with your instructor or bookstore manager.