I think the problem is when you ran your testcase last time the data may be retained in the second row and some how the contents of that row may be removed. (for ex: Clear Contents). SilkTest considers that row is filled out already. So it is inserting the data in the next empty row.
You can delete the first two rows using delete entire row.
Then retype the headers. So that the rows gets refreshed. And the data gets inserted starting from the second row.
Another possibility is your connection string. If I'm not mistaken, you can specify whether or not your first row is considered to be a header. If it is considered to be a header, then you have to insert your string into 1st row, which will result in 2nd row in the actual file.