The title pretty much explains the question. Leave it alone and let it go away, or can I scratch it off?
Leave it alone and let it go away on its own. Scratching new tattoos risks pulling some ink out, causing a patchy look. Scratching healed tattoos repeatedly risks building a layer of scarred skin which will make the tattoo look cloudy and bad. You can try some hydrocortisone cream or a very gentle wash cloth scrub if the tat is healed
