First, as a trans girl, you should be confident enough, and you should always remember that confident people are most attractive. Now you are in an open space and there are so many people around you, don't care much about what other people say or think, just be yourself. You are a customer of the store, people don't know each other here. What you should do is to look for the clothes you want and make yourself more beautiful than before.
Secondly, keep a good mood when shopping as a transgender girl. Try to make yourself look happy and kind, because people with smile are more likely to get helps from others. They may give some advice on your clothing, and it's helpful for you fo find the perfect cloth.