The oral contraceptive pill, which you have taken, is usually effective up to 72 hours as it prevents ovulation and reduces the chances of the sperm to fertilize the egg. Since you have taken the pill after 3 hours, it should be fine. However there may be a small chance of pregnancy due to certain unpredictable factors like delay in ovulation, sperms staying alive for 3- 4 days. Ovulation is the release of the ovum (egg) from the ovarian follicle. The sperm on the other hand is alive for 1-2 days but in the right environment it can sustain till 3- 4 days. Once the sperm and the ovum are fertilized, the implantation occurs after 6- 12 days. If not fertilized, the ovum degenerates within 24 hours.
In regard to your question on getting pregnant, I would suggest you to use an emergency pill like Ella which has 120 + hours action. You can take start it immediately. This should act as double protection to prevent pregnancy. Hope this helps.