You have 3 years to file your tax, and if you do not owe tax, it does not matter when you file. You should ask last year and we would have advised  you to await for the W-2 or if you had your pay check's last stuff, you would have put that information. You did not do either of them, just did it..
 Now you have to AMEND your 2008 tax, Federal as well State. Federal is pretty easy but do not know about State. But we can run on tax software and find out how it works?
How you do manually:
You have to put all w-2 and find out federal and state tax you have to pay or get refund, now you have the difference, that is what goes on 1040 amend, but you have to explain each line for the difference.