You are probably worrying too much, but I don't blame you. Coming into contact with another person's blood (especially someone you don't know) can be really worrisome. Just remember, the person whose blood it was probably didn't have HIV and they have to have had it for you to get it.
If you are worried, it wouldn't hurt to get tested, just for your own peace of mind. There are clinics you can go to anonymously. Ask them there how often you should be tested. Sometimes it's at 3 months, 6 months, or a year after exposure. I think your risk is relatively low, but if this is going to weigh on you and make you worry every time you get a sore throat, then go get tested.