Hi Prashant,
It’s understandable to feel concerned in this situation. If intercourse happened during her period and you did not ejaculate inside the vagina, the chances of pregnancy are generally low. However, it's important to know that there's still a small chance, as pre-ejaculate fluid can contain sperm.
Regarding the increased blood flow, it's quite normal after physical activity, including intercourse, to temporarily increase period flow. This happens because physical activity increases blood circulation and can cause the uterine muscles to contract more, leading to a heavier flow.
If you're worried about pregnancy, your partner can take an emergency contraceptive pill (commonly known as the morning-after pill) within 72 hours of intercourse to reduce the risk of pregnancy. The sooner it is taken, the more effective it is.
It's also a good idea to consult with a healthcare professional for more guidance and to discuss contraception options for the future.