Your stories are very confusing. Ten hours AFTER you posted this, you asked another question stating you had not had sex with your girlfriend for eight months, and you're worried about your penis fitting into her vagina.
If your girlfriend is not on birth control, and you had unprotected intercourse, pregnancy is always a possibility. Precum can result in pregnancy.
One week after her period ends is in her fertile window. Ovulation is about cycle day 14. It sounds like you are not sure if you pulled out fast enough. There is a risk of pregnancy and PlanB is advisable, to be taken within 72 hours of the incident. $50
PlanB can mess with her next cycle. A pregnancy test would now give you a definitive answer. She is not reciting a list of early pregnancy signs which is encouraging.