To answer your question: yes, your shop fucked up, and they fucked up bad.
But don't worry too much about it. 1. You can get new rivets and 2. your shop will probably buy them for you. I know that doesn't make up for the fact that it was caused by pure negligence, but if it's truly a good shop, they want your business and to make you happy. Just walk in calmly and ask to speak to the manager or owner. Don't get mad (or at least pretend not to) and that will make everything a million times easier. I work in a ski shop and trust me, when a customer is being cooperative, I tend to drop everything to try to make that guy (or gal's) day a little better. If a customer is being a complete dick and bitching and moaning, you could theoretically annoy the management and thus ruin your good relationship.
So pretty much, if the shop is worth it's salt, then they will be more than happy to help you out if you are pleasant and understanding (regardless of how mad you actually are)