I agree with fanfare, you can wait til next year to do that. When you do your next 8606, you will enter the correct amount for line 2. That will prompt TurboTax to prepare a statement to explain the correction. This will be submitted as part of your next return. Be sure to keep copies of all those past year form 8606.
I assume you are making non deductible contributions because your income is too high to make a Roth contribution.
I also assume you didn't use Turbotax(TT) in the past, as TT should have entered the correct amount on line 2 of form 8606.
