First I would suggest Combining the sentences "you are amazing" and "whether you know it or not" with a comma like so
you are amazing,
whether you know it or not.
Then I would suggest that you capitalize the first letter of the first word of each sentence like so
You are amazing,
whether you know it or not.
I love you so much.
Hope this helped!
~Just a girl in love with Shawn Mendes