Oh okay.. So some people ( not everyone.. Like 20% people ) seem to get stuck or confused on this part.. And by looking at it.. You didn't do anything wrong or get stuck.. You just didn't kill other ( the frying koopa ) on the left side.. That why the lighting still shoot at you on the left side.. You see.. In the second boss fight.. You have to finish off 2 frying koopa on both sides.. The left side and right side.. And then you can continue playing this game.. And get 3 endings.. You don't have to if you don't want to.. But I hope this helps out :)