You're willing to receive $600 but want to avoid $900 due amount towards MD States. Wouldn't be better off  if you file both returns and the refund you'll receive helps to pay the balance due?

Any Federal returns???

You were receiving paycheck from MD employer but you were NOT AWARE that your employer didn't withhold your tax from your earnings. Smell Fishy!! But the guy who just celebrated 6 years in US. 

Conclusion:  Take your responsibility and clear your tensions now.