On more recently built boats, the serial number is on the stern (that's the rear end) on the right hand side. Once you report back, we can help you how to decipher that info. You can also use the 'Search' function on this forum to find out yourself. Questions such as yours have come up before.
Visit the Yahoo! Groups sunfish_sailor page. You'll need to "join" but it's free and easy. There is a ton of good info there, including how to identify make and year. Safety info. How to rig. What's important for rec sailing and/or racing. Good luck.
That sunfish_sailor page will have tons of info to help you. Look particularly at "clonefish" type info. The moderator of that page has YEARS of information gathering into the project and I'm confident you'll find lots of useful info for your boat. I know I've seen references to that company before. Enjoy!