Hi again Sandy,
More thoughts, but on going fast this time. First thing, "fast" is relative. What seems fast now, probably won't seem as fast later on when you are more comfortable and confident at it. The transition from sailing *through* the water to planing on/over it is an exciting one, but people often feel out of control at the beginning. Comfort and confidence.
Remember, you don't have to (nor is it possible to) keep picking up more and more speed. If you are planing, you can do a few things to dump some of the speed if it is more than you care for. You can sheet out, just a little. You can head up wind a bit, which will usually slow you down.
Get in the straps and harness, go faster for a short distance, and then slow down. Practice sailing in the straps, then in the harness, then together. Learn to relax the arms and not hold on with a death grip, as tempting and instinctive as that seems to be. Once your arms are relaxed and you are countering the pull of the sail by leaning your shoulders farther out behind your hips and letting your legs do the work, and dropping your center of gravity, you'll be able to relax your brain, and will feel more comfortable.