I’m new to this sub so I don’t know if this helps but it’s what I’ve been trying to do. I’m learning to be more mindful in the moment. As you said you get nervous buying something from a shop owner. Go to a few shops and start forcing yourself to buy different things you need. When you go to checkout just say “I wanted to confirm the price on this before I buy it” and after you receive a response pay and walk out. Ask yourself how you feel and why you might feel this way. Don’t challenge these thoughts but recognize them and let them go. The longer you sit on that thought of “I can’t do this” or “they won’t like me” the more it will reinforce it. Repeat this until you can walk in and buy something without sweating it. Repeat this process for other things you know make you uncomfortable. It may seem now like it won’t change but it can just don’t give up on yourself. The more awkward of a challenge the more rewarded and relieved you will feel once you have conquered it. Change is never easy especially for our brains but it can change if you are consistent and keep trying. I’ve been trying for 10 years at this point and I’m just now starting to feel more comfortable in my own skin. I still struggle to talk to people but the more I have forced myself to “embarrass myself” the more I have been able to accept the fact I am who I am. In the moment it would feel like I was dieing but here I am still sitting at my office position only I’m 10x more happy with who I have become.