The add to cart button will only be displayed once for the first product in the record set. In order to display all the products, you will need to apply a repeat region to the add to cart button (Windows -> Server Behaviors and then click the + button and repeat region).
In the getting started guide (under "Applying Add to Cart buttons to product pages") it talk how you add to apply an add to cart button to an already applied repeat region but the process should be similar.