In order to show a message like this in your cart you would need a way to compare the value for the current item to the available quantity amount. Doing this with a recordset like this is not going to work because the first record in the recordset might not match up for the current item.
Getting this message to show in the cart is going to be a custom endeavor that require hand editing of the code to get it worked out and is not supported. One way that I can think of to do something like this would be to have the recordset and the code that checks against it inside of the eCart loop. You could then have a new recordset that is filtered for the current item on each loop of the cart. You can then have your check in place to show the message based on the recordset value compared to the value of the current item in the cart.