A good pre shot routine will cure you. If you watch all good players you will see that they follow a strict pattern and if disturbed stop and then begin again from the beginning. So practice like you are playing. For every ball start from behind, determine your target, step into position, waggle etc. Train yourself to start your swing on the same count every time. Then when you are on the course it will be easier to pull the trigger. A good pre shot routine reduces tension and anxiety which is the main reason for your problem