Worry, overanalyzing, and overthinking seems to be a fairly common trait among autistics (and if they aren't, I've got enough on my own to bring the average up).
Mindfulness techniques can help some, but I think it's mostly a matter of learning what works for you.
Here are some things that work for me:
- Think things through and then write my decision down. When I want to start second guessing myself, I remember that I have already thought it through and written my decision down.
- Recognize the patterns of thought and deliberately choose something else to think about (I can't come up with something else in the moment - I have to choose ahead of time: "The next time I start spiraling out of control, I'm going to think of this." For me, it's math or poetry. For you... ???)
- Learn to trust. Far easier said than done - sorry.
- Face the worst case and accept it ahead of time. Realize that I can make it through even if the worst case happens. Then put it aside and do.my best to make the best case happen.
- Break big problems into smaller ones and tackle them a piece at a time.
- Start doing something - anything. Even of I can't take care of everything, taking care of something make me feel more empowered and capable.
- Talking. Talking problems out with a trusted friend always helps. I almost never think to initiate social contact on my own, but when I do get it, I notice that it helps me.
- Counseling. Trying to get help to learn how to deal with this is how I got my diagnosis.
I don't use all these at all times. I kind of try whatever I think of first when I recognize that I need to do something.