Working on challenge Use Lightning Connect to create External Objects to track phone plans. Getting this error : Your organization has exceeded the maximum number of external data sources of this type. I only have 1 External. What should I do?

I have completed the activity for "Working with Custom Lightning Components" I setup "My Domain", I installed the "Contacts Today" lightning component. Added the component to the "My Data" app which was created in the prior module and saved the changes. Upon checking it through the Trailhead. It says:

Challenge not yet complete... here's what's wrong: 
The 'My Data' Lightning App was not found.

Any advice on what to do? 

Thank you in advance.