How to block out anxious thoughts and focus?

I‘ve been forced into multiple project assignments that I knew from the beginning would be too much for me. I have extremely terrible anxiety and the stress is just too much to handle. I never quite understood why people procrastinate for such big things—but now I know. Or at least why it is for me. Every time I try to start, my mind keeps screaming that I can’t do it. That it’s too much. Over and over and over. I try to ignore it, but can’t for very long as everything starts to feel hopeless and like a waste of time. At some point, I have to stop because I fear I might have a panic attack (which is quite normal for me.)

I don’t want to fail everyone who’s counting on me to complete these assignments, but I don’t know how to stop panicking over it. I don’t know how to shut out all the voices in my mind. And until I find out how, I can’t bring myself to face it. It’s like a mental barrier I can’t cross.

Some ways you all have fought through this kind of procrastination would be great. Or some tips that might work. I also have ADHD and OCD, if that’ll give anyone a better idea on how to help.