I need help. ASAP!! ADVICE 🚨🚫

My boyfriend and I are lowkey dating for 9 months. Low key meaning our parents don’t know because I got out of a shitty relationship almost a year ago and I just didn’t wanna involve my parents in this one because Iove how we are. I told my mom I’m talking to someone just to see her reaction and she lectured me to just be careful and take it slow because he is 23 and im turning 18 in less than a month. That being said, for my birthday he wants to take me to a theme park which is usually from morning to night. The whole day. The problem is, if I lie to my parents and say I’m going with another friend they’d wanna come down and tell my friend to drive safe and have fun. I don’t wanna lie and ruin the whole thing, so idk if I should just tell them “Hey I’ve been talking to this guy he treats me really good and he wants to take me to this theme park for my birthday”. I can just do that so I’m not worried the whole day that they catch me lying and knew I was with a guy, but if I do that they’d continuously judge and bug me everyday about how we are and everything. Can someone please help?? I really love that he thought of this idea for months and I really wanna go and just have a day to ourselves but idk if I should just tell my parents as it is. I mean I hope they’d see that he’s a genuinely nice guy if he’s doing this for my birthday.. please someone give me advice!