How much longer do you have to wait until 6 months?
Because I don't think at this point you will get an answer that completely satisfies your concerns.
HIV tests look for antibodies produced by the body to fight off HIV. If a test is done and there are no antibodies, then there are three possibilities:
1. The person doesn't have HIV.
2. The person has HIV but hasn't produced enough antibodies yet to trigger a positive reaction in a test
3. The person has no functioning immune system and should really be either hospitalized or dead.
It's #2 that is the kicker. Different people produce antibodies at different rates and it will take different people different lengths of time to produce enough so that any random sample of blood will contain enough HIV antibodies to trigger a test.
Practically everyone will have produced enough to test positive by 6 weeks, so the rest of the window period is really to catch as many outliers as possible.
Another factor is the probability of risk. I'm not sure if you're a man or a woman, but in general the average estimated risk of infection from what you describe is somewhere less than 1 in 2,000 for men and about 1 in 1,000 for women assuming the other person was known to be HIV-positive. If their status is unknown, then that throws another variable into the mix that decreases the likelihood.
For me, a negative 3 month test after this kind of encounter would be sufficient to say "No, you're not infected." But I'm not you. If you can hang on until 6 months to get tested to ease your fears, then do it.
Dan