Can’t widen sidebar 1

Hi

Wanted to widen sidebar 1 to bit google adsense unit 300×250. Currently sidebar appears to be 260. When I amend to 300 and save nothing seems to happen.

I pasted the code for the google adsense in the right sidebar 1 – is this the right spot!? Can’t figure out where else to put it.

Thanks in anticipation of your help.