I had sex with a girl whose periods are due in a few days, she bleeded during the process for a few moments then stopped. however the condom tore during the intercourse causing me to finish inside her. what can happen and what should be done?

Pregnancy has been documented from sexual activity during any point in a woman's cycle including during menses. It is more likely if they have irregular cycles but the risk of pregnancy here is not zero. Consider your options and decide.

There is a small risk of pregnancy. If this happened less than 72 hour ago, the girl should consider taking Plan B to prevent pregnancy. Get HPV vaccine. Wish you good health! Safe sex: https://www.hopkinsmedicine.org/health/wellness-and-prevention/safer-sex-guidelines