If my girlfriend takes the pill ritually and she just got done with her period, should we be worried about pregnancy when a little semen got inside?

Pregnancy: In all liklihood she wont get pregnant. Taking the birth control pill is very effective when taken regularly. Women usually ovulate mid- cycle, in a 28 day cycle that means day 14(day 1 is first day of period). Avoid unprotected intercourse at all times. pregnancy occurs only when there is ovulation. avoid intercourse or use condoms 3 days before and 3 days after ovulation to be safe.

No: Nothing is 100%, but if she takes all the pills as instructed, the risk of pregnancy is remote. If she misses her period by 4-5 days, do a home pregnancy test. If the result is negative repeat the test 4-5 days later unless she gets a period by then. Use first morning urine and follow the instructions for the test carefully.