Unless there is a substantial amount of vaginal fluid contact with penis through an unprotected intercourse HIV can't be transmitted.
HIV virus is very fragile and when outside the human body it starts to get deactivated.This severally reduces the viral count and making the vaginal fluids non-infectious.
I have read several cases like these in internet and experts from Dr.Bob to Dr.Hunter rate this as Zero risk. So stay happy and calm down.
Always use condoms properly and never share needles
--Chirag