Linda, sounds like the product has an EAN/Jan/UCC-13 product code instead of a UPC-A.
The EAN 12 digits is in widespread use in Europe for products. I haven't looked at the CC Shop in a while but I am really surprised that they did not make provision for a 12 digit code.
If CC is referring to the EAN or UPC as a SKU then they are technically not quite correct. SKUs are internal IDs and can be anything you, another retailer, wholesaler or manufacturer wants them to be. EAN and UPCs on the other hand are (or supposed to be) precise individual product IDs that you see as the barcodes on products.
I agree that you do not want to substitute in your shop the product EAN / UPC with something else -- Google and other search platforms do find product by their EAN/UPC IDs and not necessarily someone's SKU.
I would suggest that you drop the last digit which is normally the check digit. The item will normally be found anyway without the check digit.
Anyway, my multiple two cents....
TomH
12 digits for an EAN, JAN, or UCC-13
11 digits for a UPC-A
7 digits for a UPC-E.