You need to tie the Parameters to the parameter names in your CommandText, not to the field names with an '@' in front!
Your code:
cmd.CommandText = "INSERT INTO bene_records(f_name, m_name, l_name, b_date, add, home_num, cell_num)VALUES(@F_nameTextBox, @M_nameTextBox, @L_nameTextBox, @B_dateDateTimePicker, @AddTextBox, @Home_numTextBox, @Cell_numTextBox)"
cmd.Parameters.AddWithValue("@f_name", F_nameTextBox.Text)
...
Needs to be:
cmd.CommandText = "INSERT INTO bene_records(f_name, m_name, l_name, b_date, add, home_num, cell_num)VALUES(@F_nameTextBox, @M_nameTextBox, @L_nameTextBox, @B_dateDateTimePicker, @AddTextBox, @Home_numTextBox, @Cell_numTextBox)"
cmd.Parameters.AddWithValue("@F_nameTextBox", F_nameTextBox.Text)
...