Does anyone have any advice for my situation?

I have crippling social anxiety that has made making friends incredibly difficult. Randomly, ever since 7th grade, I have been incredibly scared about talking one-on-one with people. It has made high school incredibly difficult. Every time I see someone on the train or have to walk with a friend to do something, I get so scared and I always have to make an excuse to get away from them. I have to go with someone who I’m pretty close with to the train and take the train with them for 40 minutes tomorrow, and I am absolutely terrified. Every second of today I have been worrying about how awkward it will be and how I will lose the conversation and he’ll hate me. I used to find conversating fun — now, I never make friends because whenever I talk one-on-one with them I’m not myself. I’m incredibly boring and awkward, because every second is me in my mind trying to grip on to one conversational topic or another. It is terrible. I don’t know what to do. I have like no friends now because of this, and it feels like I can never make my voice heard because I’m always so scared it will be saying the wrong thing.