I could really use some help...a littel confused. I know that the difference quotient is f(x+h)-f(x)/h

The question in the assignment asked me to use the difference quotient to evaluate f(x)= x^2+13

this is how i did it, could you please let me know where I went wrong...

(x+h)(x+h)-x^2+13/h

x^2 +2hx+h^2-x^2 +13/h

the two x^2 are cancelled

the h's cancel, leaving 2x+h+13/2

my final anwer was 2x+h+13/h

I didn't get it correct and im not sure where I went wrong...

Thanks!