Can Chinese visa be changed after it's issued egarding to days of stay?

I bought fly ticket to china. Duration days are 63 days. But i made a mistake When I applyed Chinese visa. I filled the form only 60 day. The result is I got 60 days visa! Can I apply again and ask them a change? Will they issue me a new visa or they won't give me one? If I change my return date on my flight, I have to pay 200$ fee.
Can someone answer?