Ads

The text widget is set to be 51% of page width – so your ad is not going to fit in there.

Have you modified any theme files?

Not that I know of, how can I change that?

Re-upload a fresh, unpacked, copy of the Twenty Twelve folder to wp-content/themes using FTP or whatever file management application your host provides.
https://www.ads-software.com/themes/twentytwelve

Thats not going to affect my entire website at all?

Only if you’ve been editing the theme.

I was only asking that in case you had modified theme files – because you should not do that- your changes will be lost when WP is updated. IF you have not modified anything, no need to replace the theme files.

But to make the ads fit, you will need to make changes to at least the CSS (you have custom CSS so that’s fine) – possibly more – in which case, you’ll need a child theme –

https://codex.www.ads-software.com/Child_Themes

I have no idea how to do that.
I have not modified anything.