When things go wrong, chalk them up to experience, learn from them, and move on.
At my first startup, we won a huge order for one of our products. It was fairly simple; two floppy disks (remember them?), a manual, and a registration card, in a box. Our customer wanted thousands of copies, in batches, over a number of months.
The first batch of a couple of thousand, we assembled ourselves, creating a production line in our small office and dragging in some friends to help, paid for in pizza! It took us a couple of days and was great fun (for a while).
We shipped the completed items and our customer bundled them with their product for sale. During a random quality inspection of their finished product, they found that two disks in one of our boxes were identical! Cleary, we had made a mistake during assembly.
They called us and told us we had to go through all their products and find the matching box with the other two disks. And also check that there were no more cases where the disks were misassembled.
This took us days, sitting in their warehouse undoing the outer product packaging, finding our box, opening it and checking the labels. Then we had to reassemble their product again, without damaging anything. We eventually found our mistaken box, and amazingly there were no other errors.
After this experience, we outsourced the assembly of our product so any future issues became theirs to fix, and we could concentrate on our core business