You can generate a PDF of your invoice to see what your customer will receive. To do this:

• Go to the list of invoices
• Choose to view the details of the invoice that you would like to view
• On the "Invoice Details" page, click the 'Export as PDF" link
• This brings up the PDF version of the invoice that is sent to the customer

If you wish to tweak something, head to Settings >>Preferences>> Invoice Templates, to do so. Check this video for detailed instructions on customizing invoice templates