Yes, you should amend your return to reflect that you participate in a retirement plan so you can be properly credited for deductions, taxes, etc.
The “Retirement plan” indicator in Box 13 shows whether an employee is an active participant in your company’s plan. If this box is checked, it lets the recipient know that depending on their filing status and modified adjusted gross income, they may not be entitled to a full deduction for their traditional IRA contributions.
Since you have already e-filed or mailed the return, you
will need to wait until the IRS has accepted that return. Once they accept it and you have received your refund, then you can amend the return to correct your W-2.
If it gets rejected, you can just make the needed changes
and file again.
Please note: A Form 1040X,
Amended U.S. Individual Income Tax Return can take up to 16 weeks to process
once the IRS receives it.
After you have received your refund, please read this
TurboTax FAQ about amending your 2018 tax return: How to amend (change or correct)
a return you already filed.
