What do you get if you add tghe following code in the body of the confirm page:
EMAIL: <?php echo ((isset($_SESSION["eCartCheckoutForm_firstname"]))?$_SESSION["eCartCheckoutForm_firstname"]:""); ?> <?php echo ((isset($_SESSION["eCartCheckoutForm_lastname"]))?$_SESSION["eCartCheckoutForm_lastname"]:""); ?> <<?php echo ((isset($_SESSION["eCartCheckoutForm_email"]))?$_SESSION["eCartCheckoutForm_email"]:""); ?>>
It should display there email address. If it does, try changing the to address to only:
<?php echo ((isset($_SESSION["eCartCheckoutForm_email"]))?$_SESSION["eCartCheckoutForm_email"]:""); ?>
if that is still not working, there is likely a problem with the SMTP server. Since you say it is sending to the CC Address, but not the to address, it makes me suspect that the SMTP server is refusing to relay the email to the gmail address. check with your host to see if they can look into the SMTP server error logs and see why the SMTP server is not relaying the email.