It was the very last part before the end of the level (a friend of mine told me so).
If I use the ctrl as toggle the game is much smoother and a little bit easier. After playing it a second time I found myself keeping it always on.
I personally find it difficult when I have to jump left and then also place a block underneath me. But I get that it is one of the main mechanics of the game, so maybe I just need some more practice.
(Love the joke at the end XD)