Well that is not my only horrible misteak! 

Does this also mean the federal due date is extended? 

Be sure to complete the bank information in screen 3. and check the box for Maryland Direct ... for Electronic payment of tax due with extension. 

In screen 9 do NOT enter 1= automatic extension (for federal, because I think this will cause reject. For Maryland information check the box for e-file MD extension. and you can complete the information for the amounts as Overrides to make sure you have what you want the extension to show. This way it will not change when you finalize the return. 

When all is good, use E-File > Start Extension Wizard