Question about the 1976 movie 'Carrie'?

I love the movie Carrie, I'm watching it right now! I'm at the part where everyone is clapping because Carrie and Tommy are Prom King & Queen and Sue Snell is looking at the rope/bucket of pigs blood. Were Tommy and Sue apart of the whole plot to dump the blood on Carrie or were they just trying to do a nice thing for her and Chris and her boyfriend and the others were just being a**holes? Did Sue really ask Tommy to take Carrie to the prom to be nice? Thanks!!