Did I get Lion for free? I had downloaded the Lion beta when it was launched about a month ago. It asked me to enter credit card details and all such things, I did it.
When it was launched, I checked for the updates, there were few, it did. I didn't see what it did, I was out.   

Now if I check in Software Purchases, it doesn't show anything. How do I check if I am running Lion for real? About page says I am running 10.7!!
What you can do is to check if you are running the right build. It's just to check that you are not still running the developer preview. Lion is free for developers anyway, so that might be the reason you got it for free.