This happens when someone else is actively trying to access your account using your username.
Whether you know it (shared login) or not (unauthorized access), you should consider hiding the login page.
This can be done with free and premium (iThemes Security) plugins.
While you’re waiting for the plugin to be updated to offer this functionality natively, you can always use the “text” widget with your ad code. The text widget will also allow a headline.
The div your theme provides for the ad block is only 310px wide (your ad is 300px wide) so there’s not a lot of room for alignment.
That said, try putting your ad code in a new div:
<div style="text-align:center;">
YOUR AD CODE HERE
</div>
