The button you added has the name “Buy Now” but it’s actually an “Add to Cart” button so when you click on it the item is getting added to the cart. Since you are not displaying the Shopping cart you are not seeing the item in the cart.
If you want to place a “Buy Now” type button (a button when clicked takes you directly to paypal for payment) then use the following function:
<?php echo print_eStore_buy_now_button(1); ?>
1 is the Product ID here.