Problemas con resolución de dibujo en Adobe Fresco Ipad

Fresco is a pixel based app. It looks like you have chosen one of the pixel brushes, possibly a pencil. If you look closely at your original image you will notice pixels on the edges. When you reduce the size of an image it will feather the edges to a degree to keep the line as clean as possible. Which in effect creates the look of additional pixelation.