If you did do everything that the GNU says you need to do in order to sell the program that is fine,I havent looked at your software but if you do that then its cool, but I think that it is kinda crappy that would would charge for a program that is free, I think that is the problem that most people have with this.
As for the tutorials and games you bundled with it you should ask permission because constructs games are not necessarily covered under the GNU and even though you took the screen shot yourself it is still some one else's work that you are using for your advertisement, it would be essentially the same as me using Mario to advertise my game, and im pretty sure that I would be slapped hard and fast with a lawsuit if I did that even if I took the screen shot my self.