You have to believe you can do it. Without this belief all is lost.
Update September 2020
Good attitude is easier to maintain if you are sharing this journey with other people. You can meet other adult piano students at professional piano recitals. Strike up a conversation with the person sitting beside you. Chances are good that only pianists and former pianists attend piano recitals.
You've got to learn your instrument. Then, you practice, practice, practice. And then, when you finally get up there on the bandstand, forget all that and just wail.
I'm a professional pianist and music educator in West Toronto Ontario. I'm also a devoted student and teacher of the drums.