The reason that you are getting the same item added to the cart is because the same record is used in the add to cart server behavior. If you want to have multiple add to cart buttons on a page at once there are two choices.
You can either have a single recordset and use a repeat region around the add to cart form on the page or you can have multiple recordsets and multiple add to cart server behaviors on the page.
Which way would you like yours to be? Please post back with some details and include a copy of your current page.