We do not issue any thank-you email and download link until after the buyer's payment has completed; this is to ensure that a buyer's payment cannot be declined/NSF/cancelled after they have already received your product.
If you wish to issue downloads immediately upon completion of checkout without waiting for payment to be completed, or if you want to manually approve payments for completion but still issue the download link automatically first, you can uncheck the "Wait for PayPal..." setting in your Seller Admin > Edit Payment Preferences -- but be advised in this case that you would assume all risk of any payment failing after the buyer has already received their download.
The first part of the email you are seeing is our standard thank-you email format presenting the buyer's download link. Anything you type in the Email Message field of a product's configs would get added below our standard intro text and download link presentation.
If you wish to override our standard message entirely, and instead define the entire thank-you message from start to finish, you can checkmark the Enable Templated Email box on that same product config screen and type your message template in the Email Message box, and you can insert order-specific details (like the download link) by placing any of the following codes wherever you wish in your message template: