On your 1040-X note that line 6 says the method used to figure the tax is QDCGTW. That stands for Qualified Dividends and Capital Gain Tax Worksheet. I'm not sure why you're not seeing it. It looks like maybe you can only see that worksheet in the CD/Download TurboTax software, not in TurboTax Online.
If you want to go to the trouble, you can work through the Qualified Dividends and Capital Gain Tax Worksheet on page 36 of the IRS Instructions for Form 1040 and see if you get the same result as TurboTax. But it's extremely unlikely that TurboTax is calculating the tax incorrectly.
Doing a second amended return gets very complicated. When you cancel an amended return in TurboTax it removes the Form 1040-X, but it does not undo the changes that you made in income, deductions, etc.
By the way, under the new tax law that was passed in 2017, the cost of tax preparation software is not deductible on Schedule A for 2018 through 2025. Since you are using the standard deduction it doesn't affect your tax, but you should take that out, and certainly take it out of your explanation.
