Duplicating scenes

I am just duplicating each scene for each level and then changing them to what I want the next level to be. So I have a tab at the top for every level. Is that not a good idea? I'm asking because I got to level 7 and suddenly two of my guns don't shoot anymore. It's duplicated so that means all the code is exactly the same except for me adding an enemy to this level. So, I was wondering if just duplicating it everytime screws up the engine because you aren't supposed to do that.