Cannot modify header

I have a contact form that each time I refresh the page I get a prompt to resend all the data, I have added a header(“location: location.php”); to the bottom of the form function to try and prevent this. However all I get is a Cannot Modify Header Information – Headers already sent error. Here is my code

<?php
/*
Template Name: form-test.php
*/
include_once( ABSPATH . 'wp-admin/includes/plugin.php' );
include_once(ABSPATH. 'wp-content/themes/fiftyfityNew/contact-form.php');
get_header(); ?>

<script>
var i=0;
function test(){

for(i=0;i<=5;i++){
	document.write( "the number is" + i);
}
}
</script>
<script>
test();
</script>

<?php function make_user_feedback_form() {
    global $wpdb;
    global $current_user;

        $ufUserID = $current_user->ID;

        if ( 'POST' == $_SERVER['REQUEST_METHOD'] && !empty( $_POST['action'] ) && $_POST['action'] == 'updateFeedback' ) {
            $ufDataUpdate = $wpdb->insert( 'wp_user_feedback', array( 'date' => current_time('mysql'), 'responses' => $_POST["test"]) );
        }
        }?>
    <div id="form">
    <ol>
        <form method="post">
            <li><label for="test">Pick a date Babe:</label><input type="text" id="datepicker" name="test" value="" /></li> <!-- the (name="test") value is what the ('responses' => $_POST["test"]) value is talking too -->

            <li><input name="submit" type="submit" id="submit" class="submit button" value="Send feedback" /></li>
            <?php wp_nonce_field( 'updateFeedback' ); ?>
            <input name="action" type="hidden" id="action" value="updateFeedback" />
        </form>
    </ol>
    </div>
    <?php 

add_action('the_content','make_user_feedback_form');

header("location: http://localhost:8888/fiftyfity/?page_id=90");

?>

<?php
make_user_feedback_form();
?>

<?php get_sidebar(); ?>
<?php get_footer(); ?>