Confidence is contagious. People who exhibit confidence in what they are doing & saying are more likely to have others believe and trust in them. What you need to gain confidence in your public presence is feedback not validation. In the history of public speaking nobody has ever improved by being told “that was good.” It is through honest feedback on how you are coming across and how your message is resonating, that you will gain confidence in your public presence abilities.
A good start is to give yourself small wins. Instead of immediately setting a big goal, try setting a lot of smaller ones. You can either say “I will be a great public speaker” or instead say “I will use my voice to project enthusiasm when I speak” and “I will use the whole room when presenting to showcase my confidence.” These small goals are both definable and can be validated via feedback by a trusted source.
Find a person you trust and ask them to pay attention to your behaviors when you next present. Have them give you two things that you are doing well and two things that you can work on. This can be how you come across or the words that you are using to persuade others. It will be difficult not to focus only on what needs improving but look at the things you are doing well. The behaviors that are working for you are critical to your success. These are bright spots that you can put into the win column and continue to use to your advantage. Do not discard or diminish their importance.