I've been riding for only about 3 months now. I too fear high speeds, especially downhill.
But I don't worry, experience will fix all that. I see little improvements in my riding every week. I just enjoy riding my bike.

Yesterday while I was breezing down an open sunny country road on my bike past a field of those wonderful giant hay roll bales. Suddenly there was a big highway dept flashing sign temporarily set up there on the side of the road in the middle of nowhere.

As I pedalled past, the sign lights blinked at me threateningly:

"YOU...ARE...GOING...(blink blink blink)...13 MPH!" Too funny.

Had to stop myself from "slamming on my brakes" in an automatic guilt reaction.