Hey Luigi, I have not been 3d printing long but I have been hammering out many prints in search of the Perfect print... my suggestions on the image is as follows: - the little lumps in the print are where the 'loop' / 'layer' starts and finishes then moves up to the next leyer - the lines that i think your asking about (as you get closer to the top), is where the angle of the curve is almost too steep and there is less filament touching each other - the little stringy piece looks like it is from when the print finishes and returns 'home', the pressure in the nozzle will continue to push plastic out. I hope they help and this is not an answer from an expert, just a nooby CYA POM