Hi Elizabeth,
1) As already mentioned by other community members, the Countdown JS script is empty in your module. You need to copy the js from the countDown.min.js file included in the course resource folder as highlighted below

2) Class defined in the Countdown block's Class input parameter is invalid

3) Countdown block should only reference the Countdown js script from Scripts folder. i.e. Don't reference the same JS in screen scope.

See this demo: CountdownDemo
Refer to the attached updated oml
I hope this helps you!
Kind regards,
Benjith Sam