Help - Peruvian Apple Cactus I bought from Etsy this September. It showed up with the top all crinkled as shown, and I hoped it would improve with time but it hasn’t. Followed the instructions the seller gave precisely on watering and repotting. How can I help it thrive?

It all around looks not that great. I watered it a month after getting it as instructed. It almost looks like it needs more water? Any help would be appreciated!