String character getting deleted when I save it in the database through my web app

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C#

SQL

I have this code

con.ConnectionString = "Data Source=aaaa;Initial Catalog=aaa;User ID=aaa;Password=aaa";
                con.Open();
                SqlCommand cmd = new SqlCommand("exec doc_record @PO_NUMBER, @Path,@Time_Saved, @Scanned_BY", con);
                // cmd.Parameters.AddWithValue("@PO_NUMBER", Label4.Text);
                cmd.Parameters.Add("@PO_NUMBER", SqlDbType.VarChar, 250).Value = Label4.Text;
                cmd.Parameters.Add("@Path", SqlDbType.NVarChar).Value = NewFileName;
                cmd.Parameters.Add("@Time_Saved", SqlDbType.NVarChar).Value = "";
                cmd.Parameters.Add("@Scanned_BY", SqlDbType.NVarChar).Value = Environment.UserName;
                cmd.ExecuteNonQuery();
                con.Close();
                confirm();

What I have tried:

There is a textbox to save the PO Number. So when i enter this PO number in the text box "645-5263038-O9-SMIPLX" and press save. The letter 'X' gets trimmed everytime and it is saved as "645-5263038-O9-SMIPL" but if i enter it manually in the database then there is now problem. Before the length of the field was set to Varchar(20) but now i have exceeded it to Varchar(100) but there still is a problem.