If you registered with SONY then you can access it via the My Account / My Software link at the top of the page. If you didn't register, well then, why didn't you?
You could always call customer service and explain the situation. A little begging often does wonders.
If you've installed the program, just open the program, click on "Help", then "About .."
Your serial number will be shown under " This product is licensed to:"