My (20M) girlfriend (20F) cancelled our date because she was "sick," but now she’s planning a trip to a private house out of town with three guy friends. How do I handle this?

I’m a university student currently facing a major crossroads in my relationship. Earlier today, my girlfriend and I were supposed to meet up, but she cancelled at the last minute, claiming she had a severe headache and needed to stay home to rest. I was completely understanding and told her to feel better. However, a few hours later, she informed me that she is still planning to go on a trip tomorrow afternoon with her group of three male friends. She is the only girl in the group, and they plan to travel out of town to stay at a private house just to "hang out" because they are supposedly bored with all the local spots in our town.

​I’ve always tried to be the "chill" boyfriend; I’ve even let a previous overnight resort trip with this same group slide because I wanted to show her I trust her. I have no issue with her having guy friends or hanging out in public cafes, but this specific situation feels different. The logistics of going to a secluded private house right after being "too sick" to see me feels like a massive red flag. When I confronted her about it and asked if she would be comfortable if the roles were reversed—me going to a private house with three female friends—she couldn't give me a straight answer. She simply said she "couldn't think right" and has now been ghosting my messages for over five hours, even though I can see she is active on Discord and on a voice call with those same friends.

​I told her that while I’m not "forbidding" her from going, she needs to realize that choosing to go despite my clearly stated boundaries shows where her priorities lie. It feels like she is prioritizing her friends' boredom over my respect and our relationship security. I’m currently losing sleep over this because it feels like she’s waiting for the clock to run out so she can just leave tomorrow without resolving this. I’ve decided that if she gets in that car tomorrow at 3:00 PM without addressing this or changing the plans to something more public, I am going to end the relationship. Am I being too logical and controlling, or is this a valid boundary to set after being bailed on?