Actually, the answer isn't as simple as it might seem. The Liberty Bell goes back to the 1750s, and spelling back then was not yet exact about a number of words, including "Pennsylvania." While it was more common with two N's (after William Penn), there are some documents that only spelled it with one N, and it's also spelled with one N on the Liberty Bell. So, yes, by today's standards, the mistake is spelling Pennsylvania with only one N. But there's some evidence that in the 1750s, it was spelled both ways.