Question

TurboTax says the SSN on my W2 is wrong, but the SSN on my W2 is not wrong...

The W2 in my hand has my SSN on it, but the W2 that TurboTax "Downloaded" has the wrong SSN on it. How do I correct this?

Sounds like you need to manually enter your W2. Here are the steps:

Login and open (continue) your return in TurboTax if you don't already have it open.
Inside TurboTax, search for W-2 and then click the "Jump to" link in the search results.
If you haven't added any W-2s, proceed to Let’s start with some info from this W-2 and follow the online instructions.

(If you’ve already entered a W-2, skip to “Adding another W-2” below.)

Adding another W-2

In the Here’s your W-2 info screen, click on Add Another W-2.
A screen titled Let’s start with some info from this W-2 will display, click Continue and follow the online instructions.