I had intercourse on December 11th and my period was suppose to start December 12th. I'm now 6 days too late. Is it too early to test positive? Could I possibly get pregnant the day before my expected period date?

Any time you have sex you risk pregnancy. Now you are playing the waiting game. It is too early to take a pregnancy test. You will have to wait to see if your next period comes as expected. If not, test using first morning urine.