If you want to survive in this world, you MUST ask questions. Asking questions is not having others do your work for you. Asking questions is about learning how to do the work so that later on, you will ask questions about work that is more complex. You are inside a vicious circle - you want to appear smart and mistakenly believe that if you start asking questions, you will not appear smart, so you do not ask questions, which leads to your doing things wrong, which leads to your feeling stupid, which intensifies your desire to appear smart, which further impairs your ability to ask questions...

Do you see this? If you stop making appearing smart your goal and instead make learning the ropes your goal, you will start asking questions and get yourself out of the vicious circle.

I have not worked in retail but have worked in office environment and people like you are usually told: "There are no stupid questions. There is no shame in asking questions. There is shame in doing your job poorly because you did not ask questions and did not learn how to do it right."

Another thing for you is to try more outward thinking on the job. Instead of focusing on how others perceive or judge you, focus on noticing how they do their tasks.

I hope this helps - you clearly are NOT stupid (your post shows that), but you are very self-conscious to your own detriment.

Also, what you have been advised about structure and office jobs is worth considering in the long run, but in any kind of a job, you need to learn that it is quite OK to ask questions.