techie needed

Help! Can anyone tell me how to get my header picture to span the width of the page, so that there isn't a big white space on the sides of my Tulip Mandala. The tulip mandala, BTW, is a peice of art hanging in my dining room that I took a picture of, cropped, brightened, and uploaded. Aren't I clever? I have searched and tried, Ripp (my resident techie) has searched, found way more answers and tried...to no avail. And generally speaking, Ripp doesn't get stumped by any computer related issue. We even found the 'official' pixel measurement of the blogger header and it is still being stubborn. All of the techies at Ripp's disposal at work are entirely too busy to be bothered with my blog problem. So to the few of you who read this little 'ol blog and are computer savvy or have your own techie in your back pocket, would you please ask around. I will thank-you with cookies.