James Ford Rhodes gave this in his book, History of the Civil War, 1917:
“The steamer Nashville from New York [merchant steamer] and a number of merchant vessels reached the bar and awaited the result of the bombardment, giving indications to those inside of a large naval fleet off the harbor.” G. V. Fox, O. R. N., IV, 249;
Certainly.
A Sailor of Fortune: Personal Memoirs of Captain B.S. Osbon.
Page 118.
It appears from your source that the stopping of the Nashville took place miles west of where the shot across her bows was fired and had to do with the bombardment and the bar than the shot.