In your code to set the value of column 9, you are using a foreach loop to loop through each row, but when you set the value, you aren't setting it on the current row being enumerated.
Change your code to something like this:
foreach (DataGridViewRow row in dataGridView2.Rows)
{
foreach (DataGridViewCell cell in row.Cells)
{
if ((ActualWeight < ((1 - 0.04) * 100)))
{
row.Cells[9].Value = "LOW";
}
else if ((ActualWeight > ((1 - 0.04) * 100)))
{
row.Cells[9].Value = "HIGH";
}
}
}