set the link to pass the id value from the recordset:
mycartpage.php?ItemID=<?php echo $row_rsComp["ItemID"]; ?>
On the mycartpage.php page, create a recodrset that will filter the ItemID column of the products table on the ItemID querystring variabel.
Then add the Add to Cart server behavior. On the server behviaors panel, click the plus button and select eCart -> Add to Cart -> Add to Cart. select before page load or recordset not empty for the trigger. On the bindings tab, bind the Cart Columns to the recordset columns.