How can I let go and have fun?

I'm 17 and I've never actually had normal experiences with friends, like just hanging out, taking pictures, and goofing off. I'm pretty and everything, it's not like I'm a wierdo, but I constantly find myself rejecting offers to hang out bc I'm scared I won't be fun enough. It's awkward being around other people. I wanna know what to do to just let go and have fun and do the things others do with other people my age. I'm uptight half the time, and overthink everything. Any tips to learn how to just relax? Thanks, I'll choose best answer(: