A corrected W2 is not an option- if you paid taxes to DC, that already happened. You cannot undo that, but you need to ensure that Maryland taxes are withheld going forward (if you haven't already).
Here's what you need to do for your taxes:
-File a DC nonresident claim for refund to get all that money back. You can use Turbo Tax or complete D-40B. Your DC wages are truly $0, as the tax was withheld in error.
-Declare all of your income to Maryland. You are not eligible for any tax credits for taxes paid to DC, as you are paying $0 in tax to DC. While you wait to receive the money back from DC, you may have a tax owed to Maryland.