I had a huge problem with fear when I started earlier this year, and it still gets me now and then. There were two things that helped me - first, I found several parking lots nearby that are open and empty at times. So I'd go to, say, an office building on the weekend, when no one is there, and turn circles in what felt like safety. I'd do things like ride super fast for a few seconds and then wheeeeeeeee! to make the scary a bit more enjoyable, and I'd also challenge myself to make a circle tighter, or to stop close to a sign or tree, things like that. And the second thing I did was to take half a xanax before riding. I think I did that about 3-4 times. It bites back on the fear so you actually get to experience yourself succeeding. You CAN do it, but the fear is getting in the way. You'll see that you can do it if you don't have to fight fear at the same time. If you go the parking lot route, make sure you don't turn all your circles in the same direction. Learn from my mistake! I can make a left turn like a champ, but a right turn like I still have training wheels and don't quite trust them (okay, exaggeration but you know what I mean).
Also, don't be too shy to just drop a toe, stop your bike if you're spooked.