No problem! If you haven't done anything with one of the accounts, you can simply close it or request that it be deleted. Click on your name and image in the upper right of the site and select "Edit info." On the resulting page, select "Account" from the menu on the left. On this page, you'll see a list of your accounts for each community you have joined, and you can "Deactivate" them from there.
If both of your accounts have content associated with them, you may request that we merge the two accounts together. Email firstname.lastname@example.org with the email addresses associated with each account in order to start that process.