I am trying to be a nudist but keep getting erections!?

Ok i went in to my local woods to tey to get some freedom no one gose in the woods plus i went off the trails in to the deep part I took of my cloths and I Poped one for a good 45 min the next day i had one for about 20 minutes till it went away till I started to do some streaches. I will be going to a nudist beach in the summer need to "train" my self now i am 19 years old. help? i tryed not to think about anything too.