I am going to take a wild stab in the dark and say you didn't do a thing before trying to host a server. You simply opened Blockland, clicked Start Game, and made an internet server without any regard for port forwarding, am I correct?
If yes, I'm going to tell you to go up one level to the Help board and look up a few topics. You should see "Ω Port Forwarding: How to host an internet game".
Click on it.
