I live in one of the heavily affected states and have been self isolating for months. It has been very hard. DD is in a competitive indoor sport and they are hosting an award ceremony, inviting 100 people. Granted, the facility is very big but I think this is reckless. Needless to say, we are not going even though DD would get an impressive award. But now I am worried that people will get infected there - should we stay away for 2 weeks after to ensure that the virus doesn’t propagate? Usually, DD just trains first thing in the morning when there are only 2-3 other people in the huge facility.

OP. Before you ask - I am so confused about what the law says at the moment regarding mass gatherings that I sent an email to the city office asking what types of gatherings are currently permitted (there is no statewide ban).
I think staying away during the event is enough. I think it's fine to go in for training.
I can’t even imagine why they would host such a large gathering, against all advice. Reminds me a recent article that link non-compliance with Covid precautions to low IQ or diminished executive function abilities. Allegedly there was scientific research done to prove this...
you don't need to stay out of the facility for two weeks. assuming aerosols hang in the air for a while, they would still be harmless in 24 hours or less.