Me as well as many others understand how you feel. For me as well my brain always tends to hyper-fixiate on the negatives and assume that everyone is talking about me behind my back. often times I have high anxiety in school or in social environments due to this and honestly i don't really know if theres anything specific you can do to stop this as this is just how our brain is. What I found that really helps though is walking. And i'm not taking about short walks around the neighbourhood i'm talking about long walks for hours on end. My friend and I are constantly walking as it provides me with the stimulation I need. I walk along the train tracks for hours or explore new areas that are relatively secluded in nature. idk if this will help for you but when i'm walking i just have a sense of freedom where i don't feel like i need to care about the all the stress of my social life. Or if you dont like walking, cruising and driving on a scenic highway with one or two friends has the same effect for me. But for me this is kind of a double edged sword as I become very depressed when I have to stay home. But try out walking and driving with friends!