End of game procedure in a blow out

[kung]

I am struggled with how to end a game smoothly when there is a blow out.

Last night I had a double varsity girls/boys at a small school.

First game with home team (white) ahead by large margin with 10 sec. to go, I yell on the court, "ok white no fouls". Visitor gets the ball with 1 seconds left, pulls up for a 30 foot shoot, white get's right in her face and causes contact and I call a foul. (probably should have held my whistle). Told my partner and the visiting coach that we did not have to shoot the foul because it would not decided the game, game over. Am I right to say that??

2nd game, same situation with home having a large lead margin, I yell "ok, white no fouls". White (a late bench sub) rebounds the ball with 5 seconds and drives the length of the court and shoots a 30 footer. He get's hammered to the floor with 1 second and I swallow my whistle and walk off the court.

How do we get high school kids to understand that it is bad sportsmanship to foul or shoot a try with less than 10 seconds to play when you have a large lead. (If you watch a NBA or college game, they no how to do this)