I would have loved for this opportunity at your age, looking back now. I spent 6 years of my life proudly serving in the USMC Reserve. And I kicked myself everyday for not going active duty. I do not regret my decision to serve in ANY way, but I would have changed a few things about the way I served. I love my country, I love my Corps, I am proud to say I have served.
That being said, let me say this. First off, service is still voluntary. There is no draft. Recruiters are the only way the military has to bring in new people. I personally feel that if you don't want to join, I don't want you there. So, I will tell you this: You can get out of joining up until the point you say your oath at basic training. I could have steped off the plane in San Diego, and said, "nevermind" and they gotta get me home. Go to your recruiter, and tell him to tear up the "contract". It is not binding, they do not own your @$$. Don't let him feed you any crap. He's not going to be happy, and he's gonna try and twist you this way and that. That's his job, it's not personal.
I would hope you wouldn't have made such a rash decision. I hope your change of heart will not be regreted down the road. If you balk out now, you might not be able to change your mind back. I don't know. All I do know is that you can get out anytime up untill that final oath.
Take this Thanksgiving weekend and think long and hard about it. I don't want you to defend my freedom half-assed. You can get out, but do you really want to?
I hope this helps.
-Sean