So... internet stranger here, never met you, never met your dad never met your girlfriend, so take this with a grain of salt. This sounds like a horrible idea. Your dad, no disrespect, doesn't sound like he's emotionally or cognitively up to the task of helping you get insight into your situation, but it sounds like he has some life experience, and you might want to entertain the possibility that while he's panicking and pursuing maladaptive strategies, he might be seeing the situation much clearer than you. Lets take a look at the evidence.

Fast forward to when I'm 16 and I first meet my girlfriend.

So this is your first girlfriend, that's awesome, many people meet and stay with their first loves for a long time. But understand it's very difficult to put your anything in context if there is no precedent.

Fast forward a few years, and my girlfriend want to go to California or Washington DC, at 17. With me. At the time it sounded like a great idea, but now I realize we weren't ready

Given that you had an impulse driven by her prodding, that your dad didn't like but in retrospect you think is a bad idea, we may want to agree that you can't take for granted that your feelings or your girlfriend will lead you in the right direction every time, and that your Dad however blustery and emotionally stunted isn't always wrong.

my dad didn't like the fact that I spent nearly every minute of the day with her. She made me so happy and complete She was the feminine role model I've been needing in my life since my mom left

I mean... seriously. Can you hear yourself? This doesn't seem like an equitable adult relationship, it seems dependent and needy. Most people can't handle being on the other end of that level of dependency, unless of course they themselves have fostered it because they feed on your dependency. Your dad has called your girlfriend manipulative and controlling. This is the talk of someone who could easily be manipulated or controlled. At least think about it.