Unprotected vaginal intercourse is a risk of transmission. However, the risk of becoming infected with hiv after having unprotected vaginal intercourse with someone who has hiv is approx 1-3% per episode (though it is impossible to determine a definate figure). Given then that this occured only once, the odds are in your favour.
However, if you have not actually had an actual hiv test at least three months after the encounter, it is important you have one.
The test is definitive after three months because that is the maximum time known in normal cases for hiv antibodies to be detectable (though this usually happens within six weeks). You can rely on a negative test after three months. No other type of blood test will be able to confirm hiv status.
Try not to worry, it is not likely that you were infected, but do test.
