The last time you had sex was approximately on her ovulation time if her menses are regular ones. That means you had sex during the time she had highest possibility of getting pregnant.
Failure rate of condom is around 15 %.
This means there might be chance that she may be pregnant but there is also a possibility that she has a delayed period.
Since this is the time of her next period you can ask her to do urine pregnancy
It is easily available in any pharmacy. You just need to take a drop of urine and place it on it, and watch for the lines. Clear catalog will be given with it. It is also called as home pregnancy test.
Please confirm pregnancy as soon as possible and get an advice from a gync if you need to terminate pregnancy.