The reply to your private message is that even if the other person had blood under their fingernails, you'd still have no risk. That blood would have been exposed to air and temperature changes rendering the virus inactive. (Unable to infect)
The only answer I can give you is exactly the same one CurfewX gave you. I do agree with her that if your anxiety is creating problems for you emotionally, her suggestion that you seek therapy is the best way for you to focus on your life and not an illness you do not have. I wish you the best.
You need totally and completely FORGET about any event that doesn't involve having unprotected, penetrative sex, or sharing intravenous needles. You will NEVER have to worry about HIV if you don't do either of those.
A scratch, of course, is zero risk.
You have been here awhile now, so you should know this. I suspect your anxiety has taken over. If you continue having obsessive thoughts about HIV, please do see a counselor.