I lost a level and couldn't figure out how to end it. I ended up having to finish anyway. Can you add some clear way to abandon it after you've already lost? And make it clearer when something has already entered the circle in the middle? Nothing is worse than spending a long time finishing a level only to find out that you had already lost and didn't know it yet.
In the main menu there are two options:
1. Restart Level - same level from the beginning
2. Surrender - ending current level
I also suggest exploring this strategy: move the Awareness circle away, regenerate some Presence, then move Awareness over Thoughts to release them during out-breath. Upgrades (right click) could help as well.