...something happy to make you smile at first sight.
I'd write something cheerful, something glad.

If my happy wasn't so sad...

I'd write something happy to make us right.
Something joyful, even sappy.
Anything to make you happy!

If only my happy writing wasn't so bad...

I'd write you a laugh to make you stay. 
Would you? One more day?

Maybe a big grin,
or a faint smile however thin?

Can I make make you stay for a while, by writing you a smile?