My Dear Friend,
First thing, take out the guilt from your mind, what has happened in past you can not correct it now, you have to learn lesson from past and do not repeat the same mistake again in future.
Never ever have sex with unknown person with out a condom. You are risking your life.
Since you had unprotected sex once and the
HIV test after that is negative, that is good, but for HIV test to come positive may take few weeks.
My suggestion is you repeat your HIV test after about six weeks.
Please never ever have sex with unknown females, and that too with out a condom.
Best wishes.