a trick I learned for looking back over you left shoulder which has helped me quite a bit.
before you turn your head, make sure you have a clear path ahead, then move your right hand slightly closer to the center, lean your weight slightly onto the right arm, slightly unweight your left arm, bend your left elbow so you don't pull the handle bar to the left and then look back by leaning slightly forward with your weight centered.

I no longer have to move my right hand to towards the center but still do the lean on the right, unweight the left, bend the left and lean forward to look.

In the meantime, practice, practice, practice, on grass if you are afraid of falling.
Ride calmly, assertively and make eye contact.

Best of luck- If I can survive the streets of houston crawling with Humvees and F150 ford pick em ups, all driven by me first Texas Yahoos, anyone can survive anywhere.