How not to worry?
Simple.

You're going to die. Try to first get to grips with the fact that you are going to die. You know you're going to die, but do you really realize it?
Once you do realize that death is waiting for you, as it is waiting for everyone, and once you really realize that death is the end of your consciousness... Why worry? It's only going to cause you pain. Fix the things you can fix, and be at peace with the things you can't. You're going to die anyway, so let your efforts be directed to making you and others happier and more comfortable. That's really all that matters.