If I'm interpreting your diagram correctly(?), then the school bus made its right turn on its yellow light, which gives him the legal right of way to clear the intersection. You then entered the intersection from the bottom of the diagram and overtook the school bus before it could get back into its lane, or do I have this wrong? If that's what happened, I'd say it is you who needs to be more careful and not enter the intersection until vehicles that have a prior right of way get clear.