Well, depending on what you did, you may have to file an amended return anyway.
If you are not self-employed and you are just talking about a regular employer, the maximum salary you can defer into a qualified retirement plan (401k or Roth designated 401k) is $23,000, or $30,500 if you are over age 50. However, if you worked for the same employer, they are not allowed to let you exceed this limit. Exceeding this limit should only happen if you change employers in the middle of the year and accidentally contribute more than the allowed total. Workplace plans are reported on your W-2 and captured by Turbotax automatically, you never enter them again as if they were IRA contributions.
If you enter your workplace contributions as if they were IRA contributions, you may get a false message about over-contributing, and you may also be taking a false and disallowed IRA deduction.
There is no way to know what actually happened without having the details from your W-2 and your tax return. But unless you changed employers, it is more likely you made a mistake on your tax return that needs to be fixed before we can tell if, and how much, excess contribution you might have.
