If you spend any amount of time around naked people, you're occasionally going to see some erections. It's perfectly natural. Be cool - it won't harm you. If anyone is behaving inappropriately, or making you uncomfortable, let somebody know. Otherwise, just relax, and continue to enjoy yourself.*
*Although reasonable, this is a bit of an idealistic fantasy. In practice, you don't see very many erections at nonsexual, nudist functions. While it's true that penile tumescence tends to be relatively rare and short-lived when not in the presence of deliberate sexual stimulation, it's also a fact of life, and you'd expect to see a few on occasion. Therefore it's a bit surprising to me that it doesn't happen more often. I don't know what combination it is of the nudist demographic skewing older and larger (resulting in fewer and less noticeable erections), and people making a deliberate effort to squander any potential stimulation (as I, an otherwise easily excitable individual, not infrequently have to do) - a testament to nudists' ability to keep the atmosphere strictly PG.
I don't doubt that unscrupulous perverts (as opposed to those of us perverts who have scruples) would take advantage of a more permissive attitude, but the fact remains that practicing a more free-form version of nudism (as you can when you're alone), unconcerned with rules or the need to protect the lifestyle's image and reputation - in which you can acknowledge anything that pops up, and a sudden influx of eroticism needn't constitute a crisis situation, so much as an unexpected opportunity for an extra bit of fun - is even more relaxing and enjoyable. It has its time and its place, for sure, but let's not pretend it's any more or less than what it is.