No, you'll find one unflagged ship, approaching in low light, with no evidence that she was known to the Harriet Lane, having a single shot fired across her bow in challenge. She raised her US flag and continued to the bar. Other ships arrived during the evening and night as well and similarly stayed out past the bar, waiting for light to enter. (read the "Star of the West" reports--she did the same thing in waiting off the bar for first light. Charleston was a tricky port to enter and not one to be done with limited nighttime visibility. Here's a description from an army historical paper: "For naval forces to enter the harbor, they are required to pass through a very constricted opening near the harbor entrance. This opening is less than one nautical mile of which the majority is too shallow to allow vessels to enter without running aground. On the southern side of the entrance is Cummings Point on Morris Island, and on the northern side of the entrance is Sullivan's Island. Even flat-bottomed ships are highly constricted by this entrance. Once the ships have passed the harbor entrance, they must travel over five miles before they reach Charleston. During this transit, they must travel slowly to keep from running aground, and are, therefore, highly restricted in their maneuverability."
http://cgsc.cdmhost.com/cdm4/item_viewer.php?CISOROOT=/p4013coll2&CISOPTR=185&REC=5
Now, what merchant captain in his right mind is going to tackle that approach while the harbor is simultaneously the site of an artillery barrage?
As for "seizing commercial shipping", the only seizure you've shown was a single ice schooner, and we've established (despite your curious omission of that single detail) that this occurred after firing on Sumter had commenced.