so your parents would kill you for taking your own vehicle out of town for a couple days? Or is it their ride?
or are your parents super religious?
I honestly can't see why they would be upset. Sure, it might be weird to tell them that you're going to chill with a girl for a couple of days and all but if you're funding the trip yourself I can see 0 reason why anyone would get weird about this. My parents were always super down for me getting out of town for a few days when I was your age, regardless of the situation.