Hi there, are you talking about the GoogleAd that is escaping the side bar?
If so you can either select an advert that fits the container width which is 250px wide, their used to be a 240px x 400px banner ad with google.
Alternatively you can increase the size of the sidebar, either by increasing the container width in Customiser > Layout > Container or increasing the % the sidebar occupies in Customiser > Layout > Sidebars (you can also reduce the sidebar padding).
Let me know