Help! I don't want to bail but I'm panicking!?

So, for spring break coming up next week, I've been planning on going out of town to a place about 1,500 miles away. I am deathly afraid of flying, and that option has been crossed off the list. On a whim, I invited my friend. I don't know why I did, but I did and I don't even want her to go that badly. But she does. REALLY badly. I've told her all this stuff and she is so excited and has bought supplies and books and everything for the trip. And now, like I always do, I am panicking at the last minute. The things I'm afraid of are the long car ride (about 17 hours divided up into 2 days), being away from home, and having to stay with my friend with no escape for about a week. The car ride is what's really terrifying. And I really just want to spend time with my family, too. What can I do? I need help, fast. I'm so scared, and it's getting closer and closer and I really don't want to break my friends spirit and have to bored this spring break because of me. Now I'm getting even more panicky and I can't stand the thought of having to go! But I hinted to my friend that I don't want to go and she didn't get it..help please!!