Maybe you can knead it more to make it softer and just roll it between your hands longer until it's a smooth ball. That happens to me with gum paste but it always comes together if I roll it long enough. When I roll it between my hands I try to get the lines out by flattening slightly and then making a ball again. I repeat that motion until the ball is super smooth. I hope this helps!
Crisco does NOT make the GP less likely to crease or crack and too much of it will RUIN the GP. Adding in a bit of fondant, glycerin, or egg white will help with smoothness.
Take the ball of GP, smooth it down until the imperfections are in one spot [now the bottom]. Smooth that the best you can using your fingers. Roll the ball in the palms of your hand--not on your fingers--pressing while doing the best to move your palms in opposite directions. The result should be a pretty smooth product.
I agree, it just needed more kneading.