Thanks for writing to DoctorSpring.com with your health concern.
Your chances of pregnancy are nil, because you were on your period, and because of the Plan B too.
Regarding the backup, continue using it for the first week of the new pill pack.
After that you can rely on the pills, if you diligently take them without missing any more pills.
Do not worry about a pregnancy , and relax.
All the best & Please feel free to discuss further.