If that is your first pixel art, than I see a pixel career ahead of you! Try to give better focus to your palette control next time. Recycle colours, so you do not have any used only for one or couple of pixels, and unify all the similar ones. 64 is not bad, and great for a first pixel art. You can always use this tool http://yanrishatum.ru/pj/?input=https%3A%2F%2Fpixeljoint.com%2Fpixelart%2F140067.htm to be sure if you haven't missed any stray pixels or some colours had accidentally altered.