Not true. When the Confederate Army entered Maryland in 1862, they fully believed that the men of Maryland would rise up and join the Southern Confederacy thus seperating Maryland from the rest of the Union and cutting off Washington.
Unfortunately for the rebs, they invaded the western [pro-Union] part of Maryland, as opposed to the eastern [pro-Confederacy] part of the state. They even brought along weapons, etc, to issue the new troops they expected to raise.