I saw a napkin that had a red spot on it (before i used it). my question is can you get hiv if blood contaminates your food?

That doesn't happen: In normal everyday life, people do not catch HIV viruses by eating them. Eating the viruses does not lead to an HIV infection. That said, it's best to eat healthy, clean food. Generally, HIV is hard to catch unless a person does one of the specifically dangerous things that can lead to HIV transmission from an HIV object or HIV person. Live safely and no worries.