Everyone that cycles on open roads had at some point to work on that fear. Though a little challenging at first, it's pretty simple.

Hold your line, if you have to deviate from it make sure you use your hands to signal your intention. There's tech to help you with that too. Garmin makes a proximity sensor that you can install on your bike that you let you know when cars are getting close to you; and there's my favorite solution, a Bontrager Flare RT rear light. Finally, you should use your bike to explore alternate/less trafficked routes. Bonus tip sourced from anecdata: I've found out that if you can keep up with the traffic speed most drivers will leave you alone.

Keep cycling and have a nice ride! :)