Thank you for your concern and comment, and well in order...
Yes it was intentional for the player to be able to climb the black border of the screen.
the timer hitting zero seems to trigger the death of the character so you are indeed supposed to return to the start of the level, even if you already touched the end of the level and the animation started playing.
About the credits... I agree the animation was a bit much, makes it hard to read, not impossible but sure makes it hard XD