If you take a close look at the scoreboard at the end of the tutorial, you'll notice that it's possible to get a reclaim victory. But simply beating back the creeper with your six cannons won't do the trick. To get a reclaim victory, you have to throw your rift lab into the creeper and wait for its health to run out. Like CW3's command nodes, it will escape, and you'll be able to get it back after a little while. If you do this in the tutorial, the game will spawn a few emitters, but it will also unlock the ability to build more cannons and mortars. Then you'll be able to get a reclaim victory. I recommend giving it a try. It's like another level.