What’s the secret to happiness?

You’re right. I worry too much

Worry changes nothing.  We often care about things that have little impact on our lives, but worrying about them impacts us directly.  If I can change something that bothers me, I should do so...if I cannot, worry has no effect upon it, it only affects me. 

I need to remember this. I’ve been getting very anxious lately

Angst happens...you just need to figure out if it has a source that you can affect or not. 

I always think I can. Then worry about how I’m going to do it

It sounds more like you are putting the onus of the world upon yourself.  Whether it is large or small, there is little you can single-handedly rescue.  You can make your patch of the world better by being better; you can affect small (and occasionally large) parts of the lives of those close to you...be better;  any way around it, you should be good, imho, and then you need not worry.  

Works for me.