If you're worrying about something, one of two things is going on --
1. There's a good reason for your worries, they're justified, and you can potentially affect that outcome. If so, do something.
2. There's no good reason for your worries, they're not justified, or you can't affect the outcome. If so, stop worrying.
Easier said than done. But idle worrying does nothing of value. It makes you go crazy and doesn't make things better.
It's impossible to have perfect control of your thoughts, so worries emerge. When they do, investigate them, figure out if they're justified, figure out if you can do something, and then make a plan or let them go.
I work to be a perfect writer, a perfect friend, a perfect programmer, a perfect son and brother, a perfect motorcycle rider, and a perfect violinist. I also want to have perfect discipline, be perfect at picking where to focus my energy, and be perfect at things I don't even know how to do, like painting. At the same time, I realize that I will never be perfect at any of these things, even the ones I'm fairly good at. Some I will never be better than terrible at.
I also know that if the path to perfection were symbolized by a yardstick, I wouldn't be more than an inch or two from the start at even my best skills. That's not false modesty-- it's an acknowledgment of the impossibility of actually reaching perfection. It's so far out of reach that even excellence is very far away from it.
If there's no chance of ever reaching perfection, whats the point of striving for it? Goals can be many things-- they can motivate, but they can just as easily demoralize if you're not deliberate in how you use them. I think of goals as a guiding light, drawing me in the right direction.
If the journey is more important than the destination, then making sure one's journey is on the right path is all the more important. Having an impossible goal like perfection not only keeps you on the right path, but it focuses you on the journey. You can't look for shortcuts, arguing that the ends will justify the means, because there is no end. Instead, you see every decision in the harsh light of perfection, and are nudged towards the best path. Being imperfect, I make many mistakes and accidentally get sidetracked, but even so I move slowly in the right direction.