You will need to file a non-resident return in North Carolina to get your withholding back.
Enter your W2 exactly as it is. When you get to the state section, complete your non-resident NC return first and then your Maryland Resident return.
it populated the maryland forms before I downloaded NC. How can I remove Maryland? Or do I need to start completely over?
You need to file BOTH returns, so you do not need to remove MD or start over. It sounds like you have no tax liability whatsoever to NC if you do not live or work in the state. If you so not, then although standard practice is to file the Non-Resident state first, in this situation it won't hurt. The reason for filing the non-resident state first usually is because you claim a credit on your resident state return for taxes paid to the non-resident state.
If NC does not try to download, then you will just need to go back to the personal info section and then when asked if you earned money in another state say yes and choose NC. This should then have you add the NC non-resident return or you can click add a state when you get to the state section.
Then when you go to the NC return, and it asks for income adjustments, you will need to remove all the income from NC and leave the withholdings in place. This will allow you to get the refund for the state you did not live or work in.