i think it was this level but bob kept touching the centre wall barely and i had to redo it a couple of times, by the timer i ment that a simple colision where bob stops on colliding with a wall would have been better and did not know that a timer was already being used :p 
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Gotcha, the problem is, once Bob hits the wall, he either dies or stops and in both cases you would have to redo the level.
I've had the same issue in this specific level too, wish I'd hide the controls panel once you pick up a block to place, because there is more space than is actually visible now.