If you are considering a function I would tend to agree with Nisia-Nicole with regard to using the gazebo. Either way it would be a good idea to reach out to Gwinnett Parks and Recreation to confirm that location isn't restricted use. You might have to purchase a permit (small price) in order to use the gazebo for that purpose or put up an EZ Up. Over all the park would support a function of that size.
It may be tight for 20 people and unless you get there super earlier than planned and get set up, you may run into people already hanging out there.
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