Changed dates of travel after Chinese visa was issued

I have been issued with a Chinese visa. I was originally due to enter China on April 1st, however my plans have changed and I can only go on April 8th. When I applied for my visa, I told the embassy I would enter the country from Guangzhou on April 1st, but now I will be entering the country from Shanghai on April 8th. Does this mean that my visa is invalid? Do I need to re-apply or let the embassy know of my change of plans? the visa on my passport says it is valid until September of this year. Many thanks!