As long as your at peace about it, and believe you followed the Holy Spirit then all is good.
A lot of these "Child Porn" sites are run by Government with images of sized material. You bet the website you reported is already being tracked, if not some part of some sting operation. Groups like Watchdog have every known child porn site pegged and tracking IP address and reporting those IP address to authorities in countries that will do something. Every child porn site has some watchdog counter and our FBI are looking for a scale of things. If you continue to visit the site, then expect a knock on the door and a search warrant. If someone just finds the images in your browser cache and You did not report it, then you can have some real problems.
If you followed the Spirit of God though, then your all good. We should always obey what God tells us to do.
Mike.