Sneaking into a highschool im not enrolled in?

I have a public high school extremely close to my house but I do not attend there. My high school that I attend has a week more of summer break than the public school near me does, so I thought it might be fun to pretend to be a freshman and sneak into the public school for a bit on the school's first day. (btw I am a sopre so there isn’t a huge physical difference between me and freshmen) However, I am nervous about getting caught leaving the school or entering late. What will they do if they figure out I’m not a student there? Could there be any serious consequences of my exploration? (Serious answers only please) btw the school does not require an ID to get in and I am 15.