You should feel proud of yourself dude! You were able to finish a song and submit it which is already something a lot of people don't do, and even if you are not happy with the result, this is an experience that you will learn from and you will get better from here. I can relate to you, those are creative struggles that I believe we all go through, but sometimes we got to push through them and try to focus on the fun parts. After all, what's important is that you enjoy the process.
The disappointment will pass, so keep enjoying making music and doing what you love!❤️🔥