@beeh1126,
It's criminal trespass, yep.
And you're right that your boyfriend has more to worry about than you do. He should be getting a lawyer if/when the summons really does come although it would probably be okay for you to either share his lawyer (you can because you have the same interests in this matter and there is no conflict) or handle this matter yourself if you don't mind traveling and/or making a lot of phone calls.
If you do represent yourself, always wear nice, conservative clothes to court. Suit, modest dress, that sort of thing. It's not the place for shorts or halters or jeans. Consider it the kind of thing you'd wear to church or a funeral or a job interview. If you don't have anything like that, then go with something like chinos, decent shoes (no sneakers and no sandals), and a not too low-cut blouse without decoration (so, not a band tee shirt or a tube top, you get the idea). Cover tattoos if you can, and don't go nuts with either jewelry or makeup.
I'm not kidding; err on the side of conservatism whenever you go to a courtroom to do work.
For your boyfriend (and for you if you want to share), try to get a lawyer admitted in both states as that will be easier all around. A lawyer can get what's called
pro hac vice acceptance for one case, but that's motion practice and it's court costs and, most importantly, it takes a few months or so to get it sorted out.
Your lawyer will be able to get the venue changed and probably argue down the offense. It's likely to be a fine and there may not be much lower it can go. But a lawyer (a few hundred bucks, most likely) will be worth it for your boyfriend, who has a lot more at stake than you do.
And next time, if you want to visit an amusement park, do it when they're open and walk in and pay an admission fee like everybody else does.