"Don't let anyone, ever make you feel like you don't deserve what you want."
Think about how much you want to achieve your goal, then put your fear to the side, and keep going, one day at a time.
Besides benefitting your health in general, exercising helps memory retention, helps manage stress, and prevents depression.
Confidence is built on accomplishment. If you achieve small and big goals, you're going to feel much better about yourself.
The best way to reach your goals, big or small, is to break them into smaller goals and monitor your progress.
If you think you can do it, you can it. Don't listen to anyone, believe in yourself, and keep going.