There is a product you can buy called Stress Coat. I got it at Walmart. It's not very expensive. It's supposed to increase the slime coating on fishes' skin, prevent stress, and help with any minor scale/slime coating loss due to being caught in a net, etc. I put it in my tank when I have to net fish or do a water change. It DOES seem to help.
I honestly don't know about using it on goldfish, since I have tropical fish. I can't imagine it would hurt though, and it might help heal your fishies tail and scales. Might be worth a try?
And don't feel guilty ... accidents happen, no matter how careful we are. We all know you love your fishies and trying very hard to do the best for them.