To be completely honest with you, NO, you don not have to go. However, there was a part of you that wanted to enlist, which led you to walk into the office in the first place. Everyone gets a little nervous prior to going. you ask your self, am i doing the right thing, will i make it, or i don't want to go to war. everyone has second thought about going to boot camp.
One thing to keep in mind when you are making you decision whether to go or not. When you go to the police academy, will you also drop out before you go? You maybe setting a trend for the future. try to stick to your word, you will find out that you can accomplish anything, no matter how nervous you maybe about the new experience. this is not a lecture by any means, i just want you to understand that the recruiter worked hard to get you in and was counting on you shipping to boot camp. speak to your parent and set up a meeting with the recruiters NCOIC (Commission Officer In Charge) he will be able to help you out, he has release you from your contract.
A mans/woman's word is what make them. If they can't Trust your word, you will always be looking for a new job.
You don't want to be that guy or lady that will always ask themselves "could i have made it." Good luck in your decision