Am I ready to respond to an emergency?

Last weekend, I did a course on Standard First Aid and CPR. If there is one thing I took away from the experience, it would be the following: saving a person's life in any emergency situation is of utmost importance. Those with adequate training have a responsibility to intervene in dire situations that call for their expertise. 

All of this seems noble and Good-Samaritan like, but I'm still left with an unsettling feeling. After a weekend of training, I hardly consider myself qualified to handle an emergency situation on my own. If I make a mistake in any step of the life-saving protocol, am I not guilty of doing more harm than good on the patient even though I act out of good faith? Despite sufficient training, making a mistake is a real possibility in the heat of the moment as you race against time to save a life. 

For example, using an automated external defibrillator (AED) can help bring a patient back to life from cardiac arrest by delivering an electrical shock. Although the AED is a reliable, user-friendly, and generally worry-free device, things can still go wrong if metallic objects are not removed from the patient's body before administering the shock. These details are all too easy to miss in the spur of the moment. If death results from this negligence, you may not be held liable due to Good Samaritan laws, but can you truly escape the blame put on yourself? Can you erase the thought that, had you not intervened, the patient would probably still be alive? In this case, fear of adverse consequences and doubt about one's competency are legitimate excuses for inaction. Wouldn't it be better if someone else assumed responsibility? 

I'm at the cusp of understanding not when and how, but if, I can provide care.