This issue was a good way to understand better how rammed earth works. I removed all the part without sand layers and I just made the piece again. Humidity is maybe the most important fact. A wet piece is not going to dry and if it is not drying quickly enough it will collapse. I removed the mold and this time it stayed still better. Of course it is not perfectly straight because of the window. I understand that to make a flawless piece you need machines to ram the earth. The layers need to be extremely tight.