If your return information was transferred in from 2017, that is probably why the state return is being suggested.
First, be sure that your personal information in the My Info section of your return is set up with DC as your resident state and that you lived there all year, plus marked that you do not make money in another state.
Second, below are steps to remove a state return in TurboTax online versions:
https://ttlc.intuit.com/replies/3301384
