Remove right margin of sidebar 2

Hi,

I would ask this question on the dedicated forum, but somehow I am not being forwarded my confirmation e-mail. Hence, I am posting my question here.

I am reworking my website (www.robberdien.com) and have created a custom menu which I would like to use (the buttons on the left hand side). I would like to create the impression that this button is actually underlying the picture show of the main screen. For this reason there should be no white space between sidebar 2 and the main column. I want the button to come up right to the border of the main column.

I have looked everywhere, trying to make variations on different codes that I have seen, but none have worked… I am stuck and could really use the advise of somebody smart ??

Thanks in advance.