Filed claiming no health insurance in 2015 - turns out I was covered. What do?

To keep the story short, there was some confusion between myself and Maryland Medicaid and I thought I was dropped from their insurance. I already filed my 2015 taxes and they were accepted, but today I received a 1095-B stating I was covered all year.

Obviously I'd like to avoid the health care penalty, what should I do now?

Edit: I have been using TurboTax and filled out but have not yet mailed a 1040X, which seems like it should cover these changes to my return. Am I set with just filing this? There are other forms for state taxes as well but they don't seem to be necessary, unless I can safely ignore them I'll likely file them as well just to be safe.