You shouldn't worry about things you can't control

Also, who says I can't control it? Maybe if I keep worrying about it, I might find a solution! It's happened before!

Joking aside, this advice comes from epictetus Manual (also known as 'enichridon' or 'handbook'). It's very short, effective and (contrary to a lot of latter philosophers) very easy to read and understand. It helped me a lot fight my anxiety, you should be able to find it for free on the internets. Worth reading, in my opinion.

Third reason - you shouldn't worry but you still do...

The thing about it is, you can ALWAYS control what you want to, you'l just be punished if you do.

I've found that I mostly worry about the unknown, and if I can understand what those unknowns are, I can replace the anxiety with dread.

Your anxiety is a product of society. Society is supposed to serve human nature. We have it the other way around (human nature being forced into unnatural feeling situation to serve society).