Problem Updating Post With wp_insert_post

I am trying to change the title and content of a post, while leaving its slug and ID unchanged. Simultaneously, I am trying to save options for use in the updated post, or possibly save the modifications as metadata.

I don’t understand what I am doing, and it doesn’t save or overwrite the existing post.

Any suggestions on how to find and correct my error?

Here is my code …

<?php 

// Data to insert into post
  global $user_ID;
  $offer_3_post = array(

// Identify the post that will be overwritten
'ID' => $target_3_postid ,
'post_category'  => array($target_3_cat_id),

// Fille the new array with standard information
'post_status' => 'publish',
'post_date' => $target_3_post_date,
'post_author' => $user_ID,
'post_name' => $target_3_post_slug,
'post_type' => 'post',
'comment_status' => 'closed',
'ping_status' => 'closed',

// Fill the new array from the old
'post_title' => $source_3_title,
'post_content' => $source_3_content,
'post_excerpt' => $source_3_excerpt,
'to_ping' => $source_3_toping,
'pinged' => $source_3_didping,
'post_content_filtered' => $source_3_filteredcontent,
'post_parent' => $source_3_parent,
'guid' => $source_3_guid,
'post_mime_type' => $source_3_mimetype
);
?>

  <form action="" name ="offer_3_options" method="post">
  <b>Edit your offer description here.  Describe what you are willing to do as part of this offer. <br />(Your offer is limited to 250 characters.):</b>
  <br /><br />
  <textarea name="offer_3_t1" rows="5" cols="90" maxlength="250" ><?php echo get_option(offer_3_t1); ?></textarea>:
  <br /><br />
  <b>Enter the price or discount for your offer. <br />(Space is limited to 7 characters.):</b>
  <br />
  <input type="text" name="offer_3_n1" size="10" maxlength="7" value="<?php echo get_option(offer_3_n1); ?>">
  <br /><br />
  <b>Enter or edit the terms of any guarantee that you are offering with this special offer.  <br />(Your guarantee is limited to 150 characters.):</b>
  <br /><br />
  <textarea name="offer_3_t2" rows="5" cols="90" maxlength="150" ><?php echo get_option(offer_3_t2); ?></textarea>:<br />
  <br /><br />
  <b>Once you've made all your changes, click the button below to save your changes and then take a look at your home page and the offers page on your site to verify your edits and admire your work.</b>
  <br /><br />
  <center>
  <!-- These input fields and the submit button are copied from another page that actually "worked." -->
	<input type="hidden" name="prev_offer_3" value="<?php $target_3_post_slug ?>" />
	<input type="hidden" name="action" value="update" />
	<input type="hidden" name="offer_3_options" value="offer_3_t1, offer_3_n1, offer_3_t2" />
	<input type="submit" name="offer_3_options" value="Save Offer #3 Changes" />
  </center>

<?PHP

  if(isset($_POST['offer_3_options'])) {
  // Update the post into the database
  wp_insert_post( $offer_3_post );
}
?>