Div keep appearing at the top of the page

I created a shortcode to use within my posts so that I can create a custom message and it will appear on all of my posts.

The problem is that the message keeps appearing at the top of the post.

the function I created looks like this

function postMessage() { 

echo "<div id=\"postmessy\">Testing testing</div>";
}

add_shortcode('postmess', 'postMessage');