Hi @Jaime24805129ndnh, please share your workflow and screenshots, this could be a situation of photoshop only works in even numbers.
"Photoshop works in pixels. There are no half pixels or any other fractions of a pixel, only whole pixels.
20cm at 300pixels per inch requires 20/2.54 *300 = 2362.204 pixels. As said above you can't have part of a pixel so it has to be rounded up or rounded down. Rounding down to 2362 pixels at 300ppi gives 19.99cm. Rounding up to 2363 pixels at 300ppi gives 20.006cm"