Have you followed the link provided by USAA? You need to follow the link provided by USAA to access TurboTax along with a discount.When you get to the Review your order screen (in the File section) you'll see the discounted price along with the message Your discount has been applied.

If you have already followed the link and the discount is still not being applied you need to login to the site using Chrome Incognito Window, Safari Private or Mozilla Private Browsing and use the offer link to login to TurboTax.