Hey Sleym
First of all I would double check that you are definitely using your server's public IP address - one nice and easy way to get this is using dig from the command line:
[ricky@localhost ~]$ dig +short myip.opendns.com @resolver1.opendns.com.
213.106.96.160
And then if that's correct - I would check that port 3000 is open in your machine's firewall (I don't know what operating system you're using so I won't over-advise here). I am a familiar with RHEL/CentOS 6/7 so if you're using one of those I'll probably be able to help.
Good luck!