Bicycles are inherently stable at high speeds. You have two big gyroscopes holding you in position. The trick with any gyroscope is not to hold it too tight. If you hold it too tight, then you end up fighting it. Just have a relaxed but solid grip on your handlebars.

Also let your legs relax as well. The bumps in the road will have a bigger effect at those speeds. Just let the bike float over them under you. If you are stiff, then you end up bouncing over the bumps as if you were attached to your bicycle. Think of it like riding a horse at a gallop. You let the horse do its thing and you enjoy the ride.