Executing outside script using exec()

I have a page that makes a call to an outside php page that creates a txt file and stores it on the server, attaches the file to an email then deletes it.
 
Everything works except the bolded line of:
exec('/home/terra/public_html/CreateDealerCatalogDB.php?ID=$DealerID&save=1');
 
I initially tried using this:
<img src='/CreateDealerCatalogDB.php?ID=$DealerID&save=1' width='1' height='1'>
which worked but only after submitting twice as the <img> tag got executed AFTER the php.
 
Everything I read says the "exec()" function is what I want to do but I can't for the life of me figure out why it doesnt work.
 
Heres what I have:
 

$text = "$TransDesc \n\n $CustomizationInfo";
if($includeLogo == "1"){$path_of_logo = "../../images/dealers/dealerLogos/hires/$LogoHi";}
if($includeDB == "1"){
//create a copy of catalogDB to attach
exec('/home/terra/public_html/CreateDealerCatalogDB.php?ID=$DealerID&save=1');
$path_of_db = "../../images/dealers/db$DealerID.csv";
}
$from = "info@xxx.com";
$subject = "Dealer Order";
$email = "info@xxx.com";
$to = "info@xxx.com";

include_once('../../PEAR/PEAR/Mail.php');
include_once('../../PEAR/PEAR/Mail/mime.php');
$message = new Mail_mime();
$message->setTXTBody($text);
//$message->addAttachment($path_of_logo);
$message->addAttachment($path_of_db);
$body = $message->get();
$extraheaders = array("From"=>$from, "Subject"=>$subject,"Reply-To"=>$email);
$headers = $message->headers($extraheaders);
$mail = Mail::factory("mail");
$mail->send($to, $headers, $body);
if($includeDB == "1"){
//destroy created db
exec('/home/terra/public_html/CreateDealerCatalogDB.php?ID=$DealerID&delete=1');

And again the flow is:

• My php page executes an outside file with the path of /home/terra/public_html/CreateDealerCatalogDB.php?ID=$DealerID&save=1'
• outside file creates a txt file on my server
• php page attaches file to mail.sends
• php file deletes txt file

Any help will be greatly appreciated as i've struggled for an entire day on this already.