I'm making a 3.0 tutorial right now. I'm hoping to finish it in about a week's time. It will have the code to keep the player in-bounds from left-right (which you can then mimic for top-bottom by using y and height instead). I have the current version in this thread: http://community.stencyl.com/index.php/topic,29931.0.html
 "Stencyl 2.0 Tutorial 3: Levels & Enemies"){kind=icon}
 "Stencyl 2.0 Tutorial 1: Basics"){kind=icon}
Hello, I see that I just missed you in my livestream this morning. It's in the Scene Palette, under Game Flow.