It's good that you can pin point one of your negative thoughts
What I've learned over the years is that your thoughts cause feelings. If you think it you'll feel it.
when I did my CBT I wrote everything now. And of course it got thrown away, I wish I still had it all. But I would start with the situation that made me anxious. Such as pumping gas.
Then I would write down what I was thinking as to why it made me anxious, my negative thoughts. I don't know how to do and people are going to be staring at me and laughing because I'll look stupid not knowing what I'm doing.
Next I would go though the list of cognitive distortions, which are:
All or nothing thinking
disqualifying the positive
jumping to conclusions
magnification and minimization
labeling and mislabeling
Here's a link that explains them further http://daphne.palomar.edu/jtagg/cds.htm
I'd then pick out which cognitive distortions I was using in my thinking. For me that helped me to see that my negative thoughts really were not right.
and then I'd write my more rational thoughts about the situation. Such as everyone has to learn how to pump gas sometime, no one knows how to do it right off the bat. People there aren't going to be concerned with me, they'll be doing their own thing and not care what I'm doing. No one is going to be staring at me, and if they are maybe it's because they like my hair or my blouse.
After you go through all that you have to give yourself a little time to let it sink in. You have to read it over and over. Go over the cognitive distortions, go over your rational thoughts again and again. For me just writing it down and doing it didn't help, I had to read it over a few times.
And yes it's hard at first, but you gotta keep doing it and doing it and eventually you'll see some positive results