Pay pal return URL problem

Hai,
I integerate shopping cart to paypal i give return url after payment both sucess and Cancel url with some GET variables but the variables are not reply in paypal how to i fix this?

I set Return URL with querystring like
<input type=\"hidden\" name=\"return\" value=\"$site_url/bala/thanks.php?total=$totp&cart_id=$cart_id&uid=$uid\" />

But i got return URL from paypal $site_url/bala/thanks.php?  only Query string's are missing How to retrive this ?

My code here
echo "<form id=\"form1\" name=\"upfrm\" method=\"post\" action=\"https://www.paypal.com/cgi-bin/webscr\">
                      <div align=\"center\">
                      <input type=\"hidden\" name=\"cmd\" value=\"_xclick\" />                        
            <input type=\"hidden\" name=\"business\" value=\"$pemail\" />                      
             <input type='hidden' name='item_name' value=\"Images in DNB PHOTOGRAPHY\" />
                        <input type=\"hidden\" name=\"cart_id\" value=\"$cart_id\" />
                        <input type=\"hidden\" name=\"amount\" value=\"$totp\" />
                        <input type=\"hidden\" name=\"first_name\" value=\"$name\" />
                        <input type=\"hidden\" name=\"currency_code\" value=\"USD\" />
                        <input type=\"hidden\" name=\"uid\" value=\"$uid \" />
                        <input type='hidden' name='cn' value='DNB PHOTOGRAPHY  payment gateway!' />
<input type=\"hidden\" name=\"return\" value=\"$site_url/bala/thanks.php?total=$totp&cart_id=$cart_id&uid=$uid\" />
                <input type=\"hidden\" name=\"cancel_return\" value=\"$site_url/bala/thanks.php?total=$totp&cart_id=$cart_id&uid=$uid&fail=fail\" />                        
                          <input name=\"Submit\" type=\"submit\" class=\"colorbuttonsh\" value=\"Online Pay\" />
                          </a>
                        </div>
                              </form>";

Thanks
Bala