Well... from what you wrote, it occurs to me there are two concerns here. One is related to social anxiety & how to calm it. The other is related to habits you have developed such as playing with your hair & skin picking around fingernails.

I don't know as there is anything in particular I can suggest here myself other than to see, over the short term, if you can substitute another less obvious habit for the ones you're currently using such as "fiddling" with something like a fidget spinner instead of playing with your hair or picking the skin around your fingernails. Then, in terms of addressing the underlying social anxiety that is apparently the cause your hair playing & skin picking, you could perhaps pursue some therapy options or other techniques that might help you learn ways to better manage your social anxiety.

I think perhaps you were looking for a more concrete solution than what I have suggested... something specific you could try. I'm afraid I don't know of anything like that. Perhaps other members, here on PC, will have some suggestions. Here's a link to an article, from PsychCentral's archives, that talks about how to reverse habits such as skin picking plus 3 other articles that discuss ways to manage social anxiety:

The Golden Rule of Habit Change

6 Ways to Overcome Social Anxiety

5 Tips To Handle Social Anxiety | Being Beautifully Bipolar

Treating Social Anxiety With Meditation and Mindfulness Training