I'm not really familiar with the park or event.
Will the event be using the entire park or just a portion? If they are using just a portion and that area has been designated for their use, then IMO whoever is in charge of the event can post against carry in that area and/or as someone that is carrying to leave that area.
If the event is just at the park in general and the park is still open to the public, I don't see how you could legally be asked to leave as long as you not violating any law or ordnance.
Of course my opinion is about worth what you payed for it......