Hi,
There is never any 100% chance of transmission of HIV from HIV positive person even after completeing the sexual intercourse. On the other hand even a 15 second contact vaginal fluid of an HIV positive person can cause transmission of the infection (though admitedly the risk is very small). The chances of infection are increased if you had a skin abrasion or a cut on the areas exposed to her body fluids (mainly vaginal fluid). If you are so worried about the chances of contracting HIV infection, then you can consider post exposure HIV prophylaxis.
For more information read here...
I would advise you to discuss this possibility with your doctor.
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regards
Dr. Gupta