‘1’ should align with other list post excerpt which means that it should not affect the side widget as it does now.
please see the screenshot to understand what I mean. Thank you. https://prnt.sc/pp29gp
Apart from increasing the content width or forcing the sidebar to stack on larger screens there isn’t anything we can do to change the adverts responsiveness. All its code all comes from the adserver which you cannot adjust remotely. Maybe worth checking if there is a better banner size ad for that space.