Having a Growth Mindset is about doing things that you haven't done before. If you stay in your comfort zone then nothing will change, and you will keep getting the same results . It is completely normal to feel some anxiety or stress when you extend yourself. And the quicker you make the decision to commit the faster you will move out of the fear zone. 

The fear zone is the area you step into when you do make a decision to step out of your comfort zone. Often we will justify and make excuses as to why we shouldn't take risks. They all seem very real and if you listen to your inner-critic then you will immediately retreat back into the comfort zone.  You will not take any actions or risks and often you will experience internal conflict. 

You are now in the learning zone where you will be faced with new challenges that will extend your approach and capabilities. You will rise to these challenges and feel a sense of achievement and excitement once you overcome them. Now you have developed new skills and strengthened your mindset to achieve more and be more.