$options = get_option( 'chec_settings' );
    //Error message on line bellow
    if ( array_key_exists( 'chec_checkbox_field_0', $options ) && $options['chec_checkbox_field_0'] == '1' ) {
        echo 'Checked';
    } else {
        echo 'Unchecked';
    }

it the value is not checked it will not saved it db. so check if the array has `chec_checkbox_field_0` key.