how to widen horizontally&lessen d height for my header image on my frontpage?

I’ve used the following code to place my header image in header.php of my parent theme.

<img src="/images/guitar%20jamming.jpg” width:”100%”; alt=”” />

I’m also looking into making it clickable (to lead to homepage when clicked)

And I notice that beneath the image, there’s a thin white line after it that separates it and the next component. How do I get rid of that white line?

My site is at http://songspursuit.com/