We are in uncharted territory at this time. Is there an underlying reason that the other parent may be keeping the child? Is there someone at your home or the other parent's home that may be more vulnerable to the Covid 19 virus? I would suggest trying to talk/text/email the other parent and find out more specific information about the underlying reason for keeping the child. Reassure the parent that you are following the Corona Virus guidelines at your home. Ask the other parent when they will be willing to do the next exchange. Try to work out a schedule of FaceTime, Skype, Duo or other video conferencing with your child, during which you should only share positive messages. Do not tell the child that the other parent is keeping the child from you. Maybe you can agree on some make-up time after the stay-at-home period has ended in Maryland. This would be a good time to try some new ways of approaching co-parenting issues. If none of the above works, go ahead and file a Petition for Contempt, but be prepared to wait for the court to act. Even if we were not under this virus issue, the courts may take months to get to your case. Stay calm and stay safe.

We are in uncharted territory here. I am hoping that judges will have lithe sympathy for the parent keeping the kid absent some compelling belief that there is a greater danger upon transfer.
Another remedy besides time is atty fees being awarded.

The best you can do at this point is to file for contempt and when the courts open, they will make a decision on the amount of makeup time you will receive.

You can file for contempt, but the most the court can do is award you make up time.