So, the best advice I can give is to come clean with your doctor. I think your baby will be okay but to be safe, talk to your doctor. Plus no surprises is the baby tests positive for drugs. I'd think about how and why this happened. Make some changes to ensure it doesn't again during pregnancy or when you are a mom. Get the people in your life who offered coke to you when you are clearly pregnant OUT of your life and work on your own will power.
You need to seek advise from your Dr as soon as you can
There is nothing you can really do. You can flush "Your" system out. But chances are it will still appear in the babies body when they run test after delivery