Don't worry! This is a very simple thing to fix. You can update your first and last name at any time from your Basic Details page inside of your profile. You can navigate to this page by clicking on your email address in the top right corner of the page and then clicking on Manage Profile
From there, click on the first name field and enter your first name. Then perform the same steps for your last name. Next, click the green Save Changes button.
The first and last name fields here will update your display name for any earned certificates of completion immediately!