Even though your business is located in Maryland, if you're doing any sort of business within the District of Columbia, you are required to file a return in D.C. per this resource.
You may need to amend your Maryland return to apportion your income per the instructions on page 12 here. You would only need to report the income earned in Maryland on your Maryland return, and any income earned in D.C. would be reported on the return for D.C. See this link from the District of Columbia for more details on their filing requirements.