Can't connect to Rails server running on EC2 from public IP

I recently have been having a problem with my AWS EC2 instances. The problem is that I cannot hit my Rails servers via public IP, but I can hit localhost and the server will respond.

Here's what I'm doing:

- Create new EC2 instance (t2.micro, ubuntu free tier)

- Security group has port 22, 80, 3000 open to everyone (0.0.0.0)

- SSH to EC2 instance, install rails (I've been using this to install)

- Start rails server after install, it's running on port 3000

- run "wget localhost:3000" and it returns index.html, yay!

- go to my web browser, type in EC2 instance public IP and port 3000 (IP:3000), says it can't connect :(

- kill rails server, restart it on port 80, wget works but can't connect via public IP

- as a sanity check, I install nginx and run it, and can see the nginx start page on port 80 via public IP... so confused...

So I'm thinking it has something to do with how I'm installing Rails, but I've tried methods other than using that install script but am encountering the same problem... I've even tried creating an entirely new AWS account just in case I screwed up the settings in my original account but haven't had any luck. I have previously been able to get rails running on EC2 instances just fine (in fact I have EC2 instances using the same security group running on my AWS account right now and can hit those public IPs just fine), but am now just banging my head against the wall... any help would be greatly appreciated!