Cats don’t like me and i don’t know why

I’ve never had a cat before but I’ve been volunteering at this cat shelter for a few months. I like cats but when it’s time to pat them none of them seem to like me. I let them sniff my hand beforehand and most of the time they seem disinterested or walk away. Some of them hiss at me. I don’t know if it’s just because I don’t have experience with cats and I’m doing something wrong. I feel like the odd one out at the shelter having no previous experience with cats, and it’s making me have doubts if I should work there even though I want to continue.