AITA for not wanting my gf to go to a party?

So me and my gf (both 17) have been together for over a year and I honestly couldn’t love her more I feel like she’s my soulmate. However, my 18th birthday is coming up and we’ve had plans for a family meal and then me and her would spend time after together but that’s all changed. For context, she goes to parties quite regularly and I have no problem with it it’s just this time it’s on my birthday. Bare in mind we’ve had these plans for months, she now doesn’t want to see me after and would rather go to the party. Being honest, I don’t want to be controlling or anything but I can’t help but feel upset as I’ve been looking forward to having a nice 18th as over the years my birthdays have been horrible. We spoke about it and she doesn’t want to make me upset but she got upset at the thought of not going and made up so many reasons to go so I agreed but I can’t help but feel really upset by it. This is a special birthday and will only happen once but there will always be another party. Is it okay for me to be upset by this or am I being controlling?

(Sorry for bad explanation my first ever post)