I’m Trying To Move Out At 18 But Parents Are Trying To Stop Me

I’m 18 years old and a senior in high school, I am a Missouri resident and I’m trying to move out of my parents house before I start my last semester of high school. I’m going to be moving in with my gf 19 who lives on her own. I’ve already bought my own car, got my own insurance and everything but my parents are refusing to let me leave. My father keeps saying I can leave once I graduate but I obviously don’t want to wait that long. My father is a police officer and he says that as long as i’m in high school I can’t leave. After doing research online I’ve found multiple sources saying this claim is false. I told them a week ago I was wanting to move out and they stole $500 from me to try and stop me, so I want to leave ASAP. I wanted to come on here and verify I have the right to move out while i’m still in high school, and I want to know the legal side of them trying to stop me. Thank you in advance.