Is that situation even a risk?
They will not give you PEP for situation that you have provided.
I have read that there is a treatment for taking the medicine 3 days from the day of the suspect of the posible infection that will help in killing the virus. is it true?
If it was bleeding, and exposed to her vaginal secretions, then yes, there is a risk, as CDC mentioned in their web page on transmission. They say open wounds ( bleeding suggests that it was an open one) provide a route for HIV to enter.
Yes, vaginal fluids are included in the list of infectious fluid, so I would suggest you to go for test after 6-8 weeks of exposure. If your wound would have not been bleeding, then there was no risk.