Is it hard to get a three on the AP world exam?

If what you say is true, then you have a very good chance of getting a five. I am pretty confident getting around 70% and 5s on essays already guarantee a four or five for the final score. If your essays are as good as you say then you should have should have no problem getting a 3 or higher. Just review a little more and look for trends in the mistakes you make (such as the era and region).