HIV is NEVER transmitted in the ways you mention. If it were that simple, all the doctors, nurses, therapists... who work around HIV positive people would have been infected themselves long ago. You're OCDing your contact with that girl.
However, your problem isn't HIV, it's your extreme HIV anxiety. No doubt it will arise again in the future unless you treat it. Medication (SSRI) has helped me in the past with obsessive thoughts/hypochondriasis, but I think in your case it's very important for you to seek specific therapy for your type of OCD, or you're going to be terrified all your life regardless of medication. Right now, don't obsess with having to get better right now, it doesn't happen overnight, and yes, people with OCD obsess over things even when we know there isn't a real basis for it. Just keep repeating to yourself that you have nothing to worry about, and be aware that it's just your brain being overactive, but that your feelings of fear have no connection with reality whatsoever.
Good luck.
oh... my friend that told me the girl was HIV+ was my guy friend that I went there with... not the girl speaking of herself. Just to clarify... she didn't tell me she had HIV, a guy friend did. Sorry!