take it back and tell them what's going on? There's really not much else that can be done, and nothing else we can really advise you on, I don't think.
My macbook is about 2 years old now and out of warranty. I never bought apple care because I figured I'd be buying a new one around this time (over summer when they update the MBs/MBPs).
Well a week ago my charger started to not charge anymore and I experienced the same burning smell.
While using my macbook it started charging again.. and after about 15 minutes the area where the cord meets the magsafe, it caught fire and started to burn through. Apparently this is sort of common, it's happened to a few people, but not a mass majority.
I took it to an apple store and they replaced it for me even though my warranty was not longer
Which was really good since they're like $80
So I would definitely take it in and I bet they will replace it for you for free, especially since your MB is new.