How do you turn off the loop in GarageBand once the song is finished?

I too would like the answer to this question but I'm not sure it can be turned off.

My work-around is to extend the song with an additional song section of silence, to give me time to press the play button again to stop the song.

You may want to send feedback to Apple with a feature request to make the looping behaviour optional. use this form:

Apple - GarageBand IOS - Feedback