amalgam of numbers
Numbers? Do you mean notes?
I'm not sure if you should include this. Your description of the long hours, sore fingers, and hackneyed theme makes it sound as if you always despise those aspects of playing piano. After all, when would you enjoy sore fingers? The addition of "at times" takes away from the assertiveness and strength of this statement. However, I understand that you don't want to say that you hate piano. Ultimately, it's your call.
I am no Chopin or Debussy and since there are so many people who play, I often feel drowned in the sea of talent of other pianists.
I like this metaphor. You're missing a couple commas: I am no Chopin or Debussy[,] and[,] since there are so many people who play [piano], I often feel drowned in the sea...
whenever I audition for various competitions each year
This is too wordy. You could simply say, "when I audition for competitions," except I guess you want to convey that you participate in a lot of competitions. Perhaps "I audition for many competitions; despite my efforts, I often end up with..."?
The love-hate relationship, however, also means that the piano and I cannot get enough of each other.
I know you're trying to be funny here, but it mostly comes off as weird. Sorry.
in preparation for now and next time
What exactly are you preparing for? Future competitions? Recitals? Be specific! Saying "now and next time" doesn't help your purpose at all, and it is a waste of characters and your reader's time.
Hardships, goals, enjoyment and failure: I owe to my piano the importance of perseverance and dedication.
What? You need to connect those words to something! You could say, "Piano has provided me with hardships, goals, enjoyment and failure; it has taught me the importance of perseverance and dedication."
A solid essay! You communicate your main idea well. Good luck!
(Could you please edit one of my essays? Thanks!)