your 3 options are:
1) get ahold of a sandybridge cpu temporarily.
2) contact gigabyte and ask them to mail you an updated bios for that motherboard (it comes on a chip you replace with the one already there.)
3) send the motherboard back and get a different one which supports ivybridge right out of the box.
The manufacture date can be verified by the serial number found on the product. The first four digits after "SN" determine the year and week of manufacturing date. For example:
"4719331822101 SN082540084966" represents the 25th week of 2008