You have taken the right steps to include the amount of the excess deferral on your 2018 Tax Return.
Unfortunately, there is currently an e-filing issue within TurboTax related to excess contributions so you will need to mail in your return. You can check out this TurboTax FAQ for more information: Excess 401(k) Contribution Preventing E-filing.
Just announced: An update is currently planned for April 12th, 2019 to resolve this issue. You may still see a warning of excess contribution, but you should be able to e-file.
[Edited 04.10.2019 |1:30PM]
