I'm going to quote from this article: Combined Oral Contraceptives (The Pill)
"When you first start the pill, when it will be fully effective depends both on when you start it, as well as your own body chemistry. For most people who start the pill either on the first day of their period or the first Sunday after a period, any brand of combination pill will likely be effective after seven days of use, but here at Scarleteen, as many other credible sources suggest, we advise users to give their pills one full cycle before going without a backup to play it safe."
So, by the time this incident occured, you were either close to or at full protection from the pill. Plus, you used the withdrawl method (you can read about the combined effectiveness of those two methods here: The Buddy System: Effectiveness Rates for Backing Up Your Birth Control With a Second Method
). So, while you did have some risk of pregnancy, it was a fairly low one. At this point, if you are worried, you can wait until enough time has elapsed to take a pregnancy test.