I wouldn't worry too much about a single denial, hous. There are a lot of other companies to work with. Think of it as a job application. In the world of employment, few job applicants are offered every job they submit an application for.
For ICs it is different, because the companies are not hiring us; they are merely putting us on their contractor list and will allow us to request or self-assign their available jobs. Because most MSC applications ask so little and are so quick and simple to fill out, it's clear that most care little - or not at all - about our background, abilities, and experience. We tend to fall into thinking that, by filling out a MSC application, acceptance is automatic, because usually it is. And we tend to believe that, if the company decides to deactivate us, it is unfair and they have no right to do that or the company should explain why.
Probably there are no shoppers needed in your area or something in your demographics did not match what they are looking for. If I were in your place, I would just move on and apply with other companies. My personal opinion is that not being signed by Gapbuster is not a big loss.