Can anyone give me advice on how to be more social?

I'm really awkward in social situations. It's hard for me to know what to say to people. I spent most my childhood alone and isolated in my room behind a laptop screen (from about ages 12 to present, I'm 16 now) Just being around my step family is so awkward, I see my step sister about once a month, and my step mom maybe once or twice a week. It seems like if I say something, people don't like me, and if I don't say anything and be quiet, people don't like me. I take school online, so there's not that interaction with hundreds of kids every single day anymore, and when I hang out with my friends, unless its my best friend whom I've been friends with since 2nd grade and am very close to, I just sit there quietly and sometimes chip in when I finally think of something to say. I have a problem with over thinking absolutely everything, and social situations aren't an exception. If someone says something, I scramble for words to say and eventually they think I'm weird, too stuck up to talk to them, or something like that. I'd say I have social anxiety, but I don't exactly have the kind of dad that will take me to counseling. This social withdrawal has lead to even more isolation and withdrawal and a lot depression. It's like a vicious circle, and I'm not sure what to do. Also, don't suggest medication because when I did used to go to therapy (my mom encouraged it, she's nothing like my dad) before my parents got divorced, which doesn't bother me, they tried giving me antidepressants and I absolutely refuse. I just want to know how I can be more comfortable around people and enjoy life.