When you have more time you might go over the crack with a bit more filler to raise the level of the filler a little more even (you might even want to overfill the crack to the sides). Let it cure for about a week, sand it flush and then re- dye the dash in that area only. I was able to do a minor touch up with a soft bristle artist brush on my dash about 3 weeks after the original dyeing and it was a perfect match.