My guess would be that you are reasonably competent at your retail job. Your coworkers might take a while to get to know you, but as long as you're pleasant and do the job well, they don't worry about you.
Imagine, if you will, an introverted retail employee, quietly hanging shirts upside down and inside out on the rack. A fellow employee wanders over to inform them that's not quite the preferred way of doing it, and the introverted employee smiles politely and thanks them before hanging yet another shirt inside out and upside down, placing a clearance sign on the wrong rack, and wandering away or offering no meaningful feedback whenever someone tries to approach them about their job performance.
Being introverted is only really a problem when you don't know what you're doing, refuse to ask for help or advice, and no one can effectively talk to you about it or figure out what you're thinking.