Is it too late to upload another w2?

If you have already filed your tax return, please wait until you receive your refund - this is typically around 3 weeks after your tax return was accepted by the IRS.   Once you have received your refund you can log back into TurboTax and log back into TurboTax.com or open your TurboTax software installed on your computer. 

Then you can add the additional W-2 to submit an amended tax return - Form 1040X by mail.

Select the option “Amend a return that was filed and accepted.” and add-in the missing information.  

You can see more detailed instructions on the amendment process here: How to amend a return in TurboTax.