Why can't I get my head around motorcycles? How can I get over this anxiety?

If you have never ridden before, there is a lot about motorcycle riding that isn't intuitive. If you are cramped on the small bikes used at MSF, see if you can find a bigger bike. There isn't a huge amount of difference in the real performance these days between a 250/300 cc cruiser and a 500 cc bike. Wheel time builds confidence. IMO, you won't be a really competent rider until you get about 10,000 miles under your belt. However, just starting out, some advice. Take the MSF course, ride awhile, then take the Advanced course. Yes, they are both focused on low speed maneuvers, but that is the hard stuff. My mother could have rode a Harley at 60 mph down a highway. Learn to lean the bike in curves and learn how to counter steer the bike. Practice, practice, practice. Remember that balance is keeping your head over your butt. Watch a motorcycle race, they have their knee on the pavement, but that head is upright as much over the bike as possible. Ride at the range of your vision and quit watching the front wheel. Once you start to relax a little, the bike will go where you look, so look ahead and through those curves. Practice with the clutch, or get a bike with an automatic transmission. Honda has a number of them now, as does Aprilia.

COL Mikel J. Burroughs Sgt Randy Wilber
Suggestions?

All I can say is motorcycles are not for everyone. Your size is going to be a contributing factor. A Off/on road style dirt bike might be a better bike to look at. The hardest thing to master, is learning to use your clutch, brake and throttle all at the same time to control slow speed maneuvering. Once you master that, every thing else becomes simple. A California Hwy Patrolmen put out a video series "Ride like a Pro," it helped me out greatly. I am 6'2" small bikes make me look like a circus act.