Can't Select Champion

I just started playing league, I got to level 5 playing bots, but now I can't select any of the free champions. I'm still just trying to play AI games, and I get this message: "You cannot select this champion because you don't own them". So twice in a row I couldn't lock in a champion since I don't own any... now I have to wait 15 minutes for a new game?? This isn't my fault! D:

How can I fix this??