How to properly use wp_mail() in my own plugin?

Question

I have advanced work on my Wordpress plugin, now I need to add wp_mail(). I read this tutorial https://www.sitepoint.com/build-your-own-wordpress-contact-form-plugin-in-5-minutes/ and this tutorial work but not in my plugin.

When I use many echo all form is split apart so I cannot just write ' . esc_url( $_SERVER['REQUEST_URI'] ) . ' I used <?php echo ?> and ${}. Let give me support to my plugins work well.

echo 
    '<form action=" " method="post">
    <div id="sendmail" class="sandmail" style="display:none;">
       <h2 id="form-h1" style="color:white; background-color: #ae4a84;">Formularz kontaktowy</h2>
                
                <input id="ea-name" name="ea-name" placeholder="Imię" class="form-control" 
                pattern="[a-zA-Z0-9 ]+"  />
        <input id="ea-email" placeholder="Email" name="ea-email"   class="form-control" />
        <input id="ea-subject" placeholder="Temat" name="ea-subject" class="form-control" pattern="[a-zA-Z ]+"    />
        <textarea class="form-control textarea" name="ea-body" id="ea-body" placeholder="Treść"  >  
        </textarea> 
        <div class="btn-order">
           <input type="button" id="sendMail" class="btn-second" value="Wyślij" name="ea-submitted"  >
           <input type="button"  value="Wróć" id="btn2" class=" btn-primary"></div>
        </form>'

and php

function deliver_mail() {

    // if the submit button is clicked, send the email
    if ( isset( $_POST['ea-submitted'] ) ) {

        // sanitize form values
        $name    = sanitize_text_field( $_POST["ea-name"] );
        $email   = sanitize_email( $_POST["ea-email"] );
        $subject = sanitize_text_field( $_POST["ea-body"] );
        $message = esc_textarea( $_POST["ea-message"] );

        // get the blog administrator's email address
        $to = "@gmail.com";

        $headers = "From: $name <$email>" . "\r\n";

        // If email has been process for sending, display a success message
        if ( wp_mail( $to, $subject, $message, $headers ) ) {
            echo '<div>';
            echo '<p>Dziękujemy za wypełnienie zgłoszenia</p>';
            echo '</div>';
        } else {
            echo 'Pojawił się nieoczekiwany bład';
        }
    }
}

function cf_shortcode() {
    ob_start();
    deliver_mail();
    html_section();

    return ob_get_clean();
} 

all is in main plugin php file.