Nice game, though I kept running into one issues on the "three balls" stage. The first time I arrived there, the exists opened after only one ball was gained (all except the north exit). After that the east, south and west exist remained green despite the text still reading "two balls" - meaning I guess two more needed. But no more balls came.
And then I was sent back to the stage later, and the balls were there, the same exits green but now rebounding me when I tried to pass them. And collecting balls didn't reduce the counter.