This is a choice you have made. Some part of you agrees with this choice, believing you cannot do it, and your question indicates that you are in conflict with this choice. So have a conversation with yourself. Seriously, lock yourself in a room where you have absolute privacy, Set up two chairs facing each other. Then sit in one chair and speak out loud, telling the other “you” in the facing chair why you cannot do it. Remember to do this out loud. Then change chairs and tell yourself (out loud) why you CAN do it.
Continue this conversation openly and honestly with the two you’s until you have convinced the other side. It does not matter who wins because it is both you. The idea behind this is to listen to your reasons for both sides. Express your fears, doubts, etc. and have the other you challenge the validity of these reasons. Once you begin this process, you will be surprised how different it is than just thinking to yourself. You’ll also probably come to resolution of this conflict that will satisfy you.
If you do this and do not resolve the conflict for yourself. Have this same conversation with a therapist or trustworthy friend . Sometimes the different viewpoint about your specific reasons will be enough to help you resolve the conflict.