Empty space in the left and right margins

Hi there

I’ve all along used a screen res of 800×600 on my monitor and my blog’s theme looked fine to me.

But I just discovered that under the more popular 1024×768 screen res, my blog looked very much “thinner”, with a wide vertical space in the left and right margins.

Is there any way for me to stretch my blog’s theme out? i.e. get rid or minimize the empty spaces?

here’s my site link

thanks in advance!

Olpa