Creating a widget with a number of custom fields

I assume that you want to add more custom fields in widget back end form, for this you just need to create a new field in form( $instance ); function.

So the code will look like

        // Widget Backend
        public function form( $instance ) {
            if ( isset( $instance[ 'title' ] ) ) {
                $title = $instance[ 'title' ];
            }
            else {
                $title = __( 'Register as a candidate', 'registercv_widget_domain' );
            }

            if ( isset( $instance[ 'name' ] ) ) {
                $name = $instance[ 'name' ];
            }
            else {
                $name = __( 'Enter your name', 'registercv_widget_domain' );
            }

            // Widget admin form
            ?>
            <p>
                <label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label>
                <input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo esc_attr( $title ); ?>" />
            </p>

             <p>
                <label for="<?php echo $this->get_field_id( 'name' ); ?>"><?php _e( 'Name:' ); ?></label>
                <input class="widefat" id="<?php echo $this->get_field_id( 'name' ); ?>" name="<?php echo $this->get_field_name( 'name' ); ?>" type="text" value="<?php echo esc_attr( $name ); ?>" />
            </p>
        <?php
        }

The above code will create a new field in form. Next we will need to save/update the value of this new field in database, follow the code given below:

// Updating widget replacing old instances with new
    public function update( $new_instance, $old_instance ) {
        $instance = array();
        $instance['title'] = ( ! empty( $new_instance['title'] ) ) ? strip_tags( $new_instance['title'] ) : '';

        $instance['name'] = ( ! empty( $new_instance['name'] ) ) ? strip_tags( $new_instance['name'] ) : '';
        return $instance;
    }