I learnt how to ride a bike without training wheels when I was about 4 or 5 years old. After that I kept using my bike to go everywhere until I was 18 and got my driving license. So I can say I have good experience.
When Cycle Hire became available in London, I immediately jumped on the chance of getting a key so I can hire a bike. The first time I went to use one, something strange happened. I got on the bike, fixed the seat, checked everything and was ready to start cycling. That's when my mind kicked in and clouded everything. My legs were shaking, my hands were shaking and I could barely start peddling. I did a few yards, the bike was all over the place and I almost fell. I kept at it and when I got confident that I could do it I started cycling.
Was it that I didn't remember how to cycle? Definitely not. I had cycled for almost 15 years, so I had all the knowledge I needed. What happened was that my mind clouded my confidence and judgement. As soon as I got on the bike, I started thinking of what I had to do, what I need to be careful of, how things work, etc., etc. As soon as I got past that barrier, it was like I had never stopped (apart from the pain in my legs).
When you start working on any project, try to quiet that judgemental voice. If you have the skills and some experience, then work spontaneously without judging what you are about to do. You can review your work later. The act of creation needs spontaneity and being able to experiment. If you keep on judging yourself then you won't be able to create something extraordinary.