Although there are very less chances for a person to get HIV
with just one unprotected sexual encounter but still you should not take any chance.
The best is to go for post-exposure prophylaxis
This is a one-month course of anti-HIV drugs that, if started within 72 hours of potential exposure, may reduce the risk of HIV infection. If PEP does not successfully prevent HIV infection in someone, the presence of the PEP drugs may still reduce HIV replication until the drugs are finished. This may delay the time it takes for a person’s body to create HIV antibodies
After a one month course you can go for HIV detection tests.
Please consult your doctor as early as possible and start PEP.