Where would i add that i bought a car last year that i forgot to mention on my taxes?

To add a vehicle:

You enter it in the Estimates and Other Taxes Paid section of TurboTax (which is under Deductions and Credits).  You'll see the line for Sales Tax.  As you go through the EasyGuide questions you'll be asked about major purchases.  This is where you'll enter the sales tax info on your new vehicle.