If you haven't yet submitted your return, you need to get that W-2 before you do so. Call the company and tell them to send it to you.
It's usually not a good idea to use the figures on your pay stub, as these do not include taxable benefits and other things.
If you absolutely cannot get a W-2 in time to file, then you need to call the IRS. They will probably tell you to file Form 4852 with your best estimates of what should be on the W-2.