Can't point Dreamhost DNS to Amazon EC2 instance

I first created a hosted zone on Amazon Route 53, and the config is as follow:

example.com A 52.xx.xxx.xx
example.com NS (already given)
example.com SOA (already given)
www.example.com CNAME example.com

Then in DreamHost, I change its whois nameserver to the ones given by Route 53, and I also created a custom DNS record:

Dreamhost whois nameserver config

Dreamhost custom DNS record config

But when I access my domain name, it says Site Not Found.

Can somebody help ?