Bitnami Node Stacks are designed with Apache in front acting like a proxy to the Node server behind listening in port 3000 or any other. Using this configuration you can access your node application on default Apache server port 80.
You can find how we do it installing Bitnami Ghost Stack and looking to the configuration files.
If you are testing your node application maybe you dont want to mess around Apache proxy configuration and just want to access your node application using port 3000.
Probably you cannot access port 3000 because you have not opened it in Amazon Console. By default Amazon opens 80 (http), 22 (ssh) and 443 (https).
Can you check your instance preferences in Amazon Console?