Badly formatted html wreaking havoc :(

I'm having a problem with this plugin and I suspect it's due to my badly formatted html code I put in the Ad Code field.

I can't delete the "badly formatted code" because the Ad Code (which has a link to another site) has screwed up the"Save changes" and the "Reset" buttons. They now link to this "other site", so they don't work.

Deactivating/reactivating the plugin doesn't work AND Reinstalling the plugin doesn't work either, because that badly formatted code reappears.

I'm guessing that the Ad code that I entered still remains in the database even after the plugin is deactivated and deleted.

I'm also guessing that my only option is to delete the database entry... but where would it be?

Is this the only way to fix the problem?