See how to create your own highscore scoreboard in this experience.
Each coin adds a point to the Score variable while the Countdown Timer decreases. When the Timer reaches 0, the session will end and the score variable will report how many points you were able to score.
Look for the "Report Score" event on the Score variable in the scene. It reports the score when the Timer runs out.
If you want to use this set up for you own games, make sure to set up a scoreboard on the game's webpage after saving it. Otherwise your players won't be able to report their scores!