New guy here, but I have watched as many tutorials on youtube as I can find and read through the forums to try and fix I'm on BB3b3 and my scenes are not starting/stopping at the endpoints. They overlap which is causing obstacles and object to double up on each other, making the game impossible to play.
When creating levels I would suggest copying the start scene to use the same background for all scenes. Take a look at the Flap template. Once you have the background and floor set up, use the scene to make more copies and adjust objects to create different scenes.