There are no mistakes in music, that's very subjective, it really depends on what you intend to do and I don't see any mistakes here.
Technically this is a good piece, but it's not your style, it's mozart/beethoven style and they have already perfected it. I like when people write in their own style, it's always fun and interesting and so if you have other music that is more of your style, please share I would absolutely love to hear, even if you think it's not "perfect".
And It's just my opinion and I am no expert. if you don't agree just scroll and ignore this forum, don't take it personally.