Is there a substantial chance of pregnancy?

hi. my girlfriend is on the birth control pill ortho tricyclen lo and she takes it very methodically.  her prescription was not ready at the end of her last cycle and therefore missed one day between cycles (friday cycle ended, resumed sunday.) and took the pills on a regular basis since but did not double up for the day she missed.  the next saturday (6 days later) we were about to have sex and i put the head in side of her for approximately 2 seconds and quickly withdrew.  i did not come. then we proceded to have sex with a condom.  i am however nervous about the possibility of precum causing a pregnancy and the relevance of her skipping a day in between cycles? is this enough to completely throw off the pill's pregnancy preventative measures? please help.