How can I make this sonnet sound better?
It doesn't adhere to the rhythm of a sonnet. It doesn't rhyme. Your syllable count is off. It's redundant. Anything you do aside from adding to it would improve it, including burning it.
O, yellow sun so shiny bright and gay, Yet careless in its size and warming smile; The eye of heaven opens up the day
That's not a sonnet. To make it a sonnet, try writing it in iambic pentameter, employing three quatrains and a couplet, and following an ABABCDCDEFEFGG rhyming scheme. This is a sonnet: Nirvana: The Last Soliloquy of Kurt Cobain by Belo Braga My LOVE is like a stone inside my heart whose cold and heavy granite marks my grave. My body yields no wisdom to impart, for here there lives no man inside to save. My LOVE is like this needle in my arm, whose rusted tip pollutes my sanity, and tears away all hope with lethal charm, so she and only she is all I see. My LOVE is like a stain upon my soul whose evil murdered all the good in me. I now am only but an empty hole; her fetid filth is my eternity. My LOVE is like this gun against my head; she drags me down to Hell and leaves me dead.