You already know the problem -- you're using front brake when the wheel is turned at slow speed, a 100% guarantee you're going down unless you have the reactions and strength of Superman. Concentrate on using rear brake only when maneuvering at slow speed. Even straight-ahead stops go better if you ease off the front brake as you go completely to rear just before the bike stops. That way, slight front-wheel displacement won't dump you at the stop, and you'll stay a lot more stable during the entire maneiver.