OP, you cannot
change your personality. There are all sorts of leaders. Not all of them are take-charge, in-your-face people. Some are more thoughtful and soft spoken but that doesn't mean that they are not effective. Great leaders are people who can inspire others to believe in a shared vision. Responding quickly to emergency situations is not a test of leadership
... it is a test of technical know-how & confidence.
I would like to encourage you to do some self exploration. Start with 'Now, discover your strengths'. (Amazon.com: Now, Discover Your Strengths (9780743201148): Marcus Buckingham, Donald O. Clifton: Books
) I use it in leadership development programs. It's a quick read that also includes a self-assessment tool that you can do online. I love this book, because it really helps you identify what's 'right' about your own personality and points out the most effective ways to deal with others.
I would then urge you to establish a mentoring relationship with a nurse leader. If your organization does not have a formal program for this, then arrange it on your own. Seriously - most leaders are very flattered to be recognized for their talents and happy to help others develop. There's a neat little book called "Connecting: The mentoring relationships you need to succeed" (http://www.amazon.com/Connecting-Men...425216&sr=1-19
) that is a great guide to beginning this process.
Finally, if you do not have a graduate degree, go ahead and start moving in the direction of your MSN. This process will help you develop confidence as you increase your skills and knowledge.