To get hiv from blood contact, open sore means what? deep bleeding cut or superficial cut or surface cut .

All of the above: An open skin surface makes direct transmission possible and the deeper the cut , the more contact with the blood.

Low risk, no worries: I suspect you are over-interpeting the term "open cut" and its association with HIV. To my knowledge, except for injuries of medical personnel with HIV contaminated sharp instruments, there has never been a reported case of HIV that was believed to have been aquired because a cut was exposed to the virus. There has been no research on exposed cuts and HIV risk, but it's mostly just theoretical.