I Created a web app in SharePoint 2013, and a site collection as well. But when I am about to open the page I get this message:
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I made this same mistake and selected the two key users who would be administering the site in the future, assuming my domain admin account would still be able to log into the site.
In Central Admin, go to Application Management > Change site collection administrators.
Set one of them (primary or secondary) to yourself.